Warmth and Showers Leading Up to Christmas

    Winter officially begins on December 21st, but it will feel a lot more like October over the next several days, as temperatures increase throughout the week, culminating in what will likely be record-shattering warmth on Christmas Eve.  Through December 19th, Philadelphia is 11.2° above average for the month, and above average temperatures will generally be the main story through the end of the year.  The period of December 10-18th saw temperatures of 11-24° above average itself, and no day this month has been below average thus far.  Below is my forecast for our holiday week, with still some uncertainty for rainfall totals on Wednesday and temperatures for Christmas Day.

Monday

  As a weak cold front approaches from the west, it will dissipate and 'likely' leave us dry.  We'll see a gradual increase in clouds through the day, with partly/mostly cloudy conditions in general.  Our week of mild temperatures will begin with a high of 55-60°.

Tuesday

  An upper-level disturbance moves through the Northeast and brings clouds and the threat of showers for the morning/afternoon, with any precipitation likely ending by sunset.  We'll likely see upward of a tenth of an inch or so, with a high of around 60°.

Wednesday

  A frontal boundary approaches from the west, a warm front will move through the area, and precipitation will overtake the area.  Periods of showers and rain will fall throughout the day as a low pressure system strengthens over the Great Lakes, providing for windy conditions as well as rain.  It appears at this time, with upward of 0.50-1.00" possible and a high in the mid-60's (Philadelphia's record high is 66°).  Below is modeled radar for 4pm on Wednesday:

Modeled radar from the NAM for 4pm on 12/23 (Image courtesy of TropicalTidbits.com)

Christmas Eve

  Any lingering showers end by the afternoon, and high pressure from the west should begin to dry things out with some clearing.  We'll likely remain breezy, as temperatures soar to 70°+ (current trends are for the low- to mid-70's!).  The record high for Philadelphia is 64°, and it's looking like this record will be shattered.  Below is the GFS MOS Data that shows modeled record temperatures for Thursday:

Christmas Day

  High pressure will continue to build in to provide for a dry and mild holiday, with temperatures still uncertain but likely nearing 60°, but it really depends on the timing of our frontal passage.  

  

Record Warmth This Weekend

    The past month and a half have certainly had plenty of warmth, as winter-haters rejoice and snow-lovers weep.  November was 5.6° above average in Philadelphia, and so far through December 10th, the city is currently 7.0° warmer than average.  Coincidentally, that number will increase through the weekend thanks to temperatures that will likely set records.  The record high for Saturday & Sunday in the Philadelphia area is 65°, with Monday's being 69°.

    Ahead of an approaching system from the west, a ridge will build in across the Northeast for the weekend, allowing for warm air and moisture to build into the region.  The process that will help cause these abnormal temperatures, called warm-air advection, is the transport of warmer air by the flow of the atmosphere.  In our region, this usually happens with a southerly flow, which brings warmth and moisture from the Gulf Coast, which is what we'll be seeing through Monday.

    For our Saturday, morning fog will give way to a mostly to partly sunny sky, with calm, dry conditions and a high in the mid-60's.  Sunday will then be much of the same with even warmer highs into the upper-60's, and some places could even threaten the 70°-mark!  Below is GFS data showing highs well into the 60's and approaching the 70's when our average high is only in the mid-40's.

GFS MOS data from Friday showing record warmth this weekend!

    However, all good things must come to an end, as clouds will increase on Monday with that cold front approaching from the west.  Though the region will continue to see highs well into the 60's, showers will be the story for the PM hours, with upward of a half an inch of rain possible at this time.  On top of the warm temperatures and rain threat, windy conditions will be in play due to the pressure difference between the strong low pressure over the Great Lakes and high pressure off the coast.  Breezy conditions will continue into a beautiful and slightly cooler Tuesday.  Below is the GFS (American) model's look at Monday's rainfall for Monday late afternoon/evening.

Friday afternoon's GFS model run showing Monday's rain threat.  Image courtesy of TropicalTidbits.com

Cinnaminson Day Forecast

    Heading out to Cinnaminson Day on Sunday?  Here's a detailed forecast for the chilly day:

Morning (Through Noon)
    Temperatures early in the morning will be reaching a low in the mid-30's, with some area even approaching the freezing mark.  With high pressure continuing to build in from the west following Friday's cold frontal passage, winds out of the northwest continue to bring colder into the area.  We'll see mostly sunny clouds for the morning hours, with winds beginning to strengthen toward mid-morning (10-15mph).  Temperatures will increase from the mid-30's around sunrise into the 40's by late morning,

Afternoon (Noon-5pm)
    Temperatures will continue to climb to a high of around 50° for the afternoon hours, with clouds increasing to partly sunny skies.  Winds will also be on the increase, with 10-20mph winds and gusts to 30-35mph, which will not help with how chilly it'll feel, even with a good amount of sunshine (it'll feel like the 40's).  Finally, with some upper-level energy passing through the region during the PM hours, there will also be the slightest chance of a shower which can not be ruled out, but it will certainly be mainly dry.

Evening (After 5pm)
    Clouds decrease through sunset as temperatures begin to tumble, as it'll fall back into the 40's by nightfall.  Winds will also fall off through the evening time frame, with mainly clear skies.

Season's First Cold Blast Incoming

    It looks like we'll be in store for this season's first cold air blast this weekend, as winter-like temperatures overtake the Northeast.  A weak and moisture-starved cold front moves through tomorrow, with high pressure building in behind it.  Ahead of the cold front today, we had relatively warm air, with highs in the 60's, helped out by winds out of the west and southwest.  However, winds shift out of the northwest tomorrow, which generally occurs behind cold fronts, and will bring colder air out of Canada.

    This wind out of the northwest will pull down the colder air out of Canada (called cold-air advection) and will bring temperatures in the 50's during the day and 30's at night for the Philadelphia Metro area.  As you can see from the MOS data below, low temperatures will fall into the lower-40's Friday night, but the truly winter-like air will be in store for us on Saturday and Sunday night.  Clear skies and calm winds are the perfect combination for cooling, and we'll probably only see one of those Saturday night, with mainly clear skies and still a little breezy, leading to lows in the mid- to upper-30's.  Breeziness calms a bit more for Sunday night, which will allow for our lows to approach freezing, so watch early Monday morning for the possibility of some frost.  The typically colder areas, especially to our north and northwest will even fall into the 20's during this time!

GFS MOS Data for Mt. Holly, NJ showing lows in the 30's for this weekend!

    During the daytime, we'll see mostly sunny skies Friday through Monday, with highs decreasing throughout the weekend.  Highs Friday will rise back into the 60's but go downhill from there.  Highs only reach the mid-50's Saturday, with breezy conditions, while Sunday and Monday see highs only reaching into the lower-50's and around 50° throughout the area.  Though we'll see dry conditions likely through Monday, higher elevations and areas of Northwest New Jersey through Central Pennsylvania will have the threat of some snow/rain showers on Sunday, with temperatures allowing for that threat.  This can be seen in the image of the GFS model run below, displaying rain/snow showers across parts of the Northeast on Sunday.  If you hate the cold, don't worry, because temperatures look to rebound next week.

This afternoon's GFS model run showing rain/snow showers Sunday for some areas
Image courtesy of TropicalTidbits.com

Drought Relief With a Rainy Week Ahead

    Dry dry dry...New Jersey has actually been in the midst of a minor drought, with much of the state in the lowest category of "Abnormally Dry" and parts of Northeast New Jersey in a "Moderate Drought", which can be seen in the image below from the "United States Drought Monitor" website.  However, it appears that this is going to take a drastic turn this week as we keep an eye on multiple threats for rain this week.  We'll see the possibility of a whole package of weather for the upcoming week, with rain, cooler temperatures, windy conditions, flooding, and coastal beach erosion all affecting New Jersey by the end of the weekend.

Northeast Drought Conditions as of 9/22/15 (http://droughtmonitor.unl.edu/Home/RegionalDroughtMonitor.aspx?northeast)

    Tomorrow, a low pressure system will approach from the southwest as a cold front moves toward the area, with our last day of warmth (around 80°) and high humidity before it drops off on Wednesday.  The low pressure center will ride along the frontal boundary and begin to being showers after nightfall, though an isolated shower couldn't be ruled out during the day.  The boundary will then stall near our area as it passes through on Wednesday, and periods of showers and moderate to heavy rain will likely fall throughout the overnight hours into the daytime hours.  Depending on exactly how strong this low is and where it sets up, we could be looking at up to 1-2" inches of rainfall through Wednesday night, with areas of higher amounts across the region (especially into Northwest NJ and Central PA).  Below is an image of forecasted rainfall totals through 8pm on Wednesday.

Weather Prediction Center Forecasted Rainfall Amounts Through 8pm Wednesday

    Though the front stalls near our area, we'll be on the cooler side behind it, with temperatures falling into the low- to mid-60's for highs to end the week, with winds beginning to whip up out of the northeast.  A strong high to our north, and developing low pressure to the south, will create a strong pressure gradient to produce 10-25mph sustained winds (higher gusts) off the ocean Thursday and through the weekend (strongest winds along the coast).  This will be a cause for concern along the coast, as strong beach erosion and coastal flooding will likely occur.

   Also, this stalled front will allow for continuous areas of showers to affect the region on Thursday into Friday, with mostly cloudy conditions continuing.   Friday/Saturday will become interesting as the week wraps up, as we watch the track of what will likely become Tropical Storm Joaquin (currently Tropical Depression Eleven).  The National Hurricane Center currently has it forecasted to be off the coast of New Jersey on Saturday (image below), allowing for windy and wet weather to persist into the weekend.  Right now, it looks like a trough over the eastern US and a high to the east will allow for the system to ride along or even make landfall in the Northeast, but a lot can happen between now and then.  Though, by the end of this weekend, some places could be looking at rainfall totals of several inches or more. 

    By the start of next week, it looks like high pressure will provide a rebound to more settled and beautiful weather!

The National Hurricane Center's Current Track for Tropical Depression Eleven

Rain and Storms for Thursday

    Summer still has two weeks left, and our recent weather is certainly proving that.  We're coming out of an August that provided for plenty of sun, heat, and humidity with little relief in the way of rainfall.  Consequently, we have had two heat waves in less than two weeks entering September!  The Philadelphia metro area was bone-dry, with less than an inch of precipitation for the whole month of August, 0.98" to be exact.  However, the region will likely see that total and more just within the next 48 hours as a cold front moves through, along with a low pressure system riding along that boundary.

    As the front approaches tonight, a line of widespread showers and storms will begin to affect the area after midnight.  Our current instability in the atmosphere will allow for thunderstorms and periods of heavy rain to occur throughout the overnight hours and during our Thursday.  This will result in a long-lived soaking of the state, which is currently in the beginning stage of a drought, in the category of "Abnormally Dry".  The instability drops off by tomorrow evening, leaving us with periods of just showers and heavier rain, without the storm threat.  Below is a modeled look at radar for tomorrow at 6pm from the afternoon 4km NAM run.

18Z 4km NAM model run (9/9/15)...courtesy of the PSU E-Wall

    Humidity will stay with us tomorrow, but the temperature will plummet compared with the past few days, with a high in the lower-80's.  Along with this drop in temperatures, periods of heavy rain and storms will fall throughout the day and into the evening.  As nightfall approaches, rainfall will likely become less numerous and widespread, with the threat of rain gradually dropping throughout the overnight hours.

    By early Friday morning, we'll just be dealing with the chance of some lingering showers of the scattered variety, as clearing occurs and we see a mix of sun and clouds for the day.  The heat and humidity will be gone, lasting throughout the weekend and into next week.  Regardless, we should be completely dry by the afternoon on Friday but not before the region sees much-needed rainfall.  Total-wise, most will see upward of 1-2"+ of rain, with some locations receiving more under repeated heavy banding of downpours and storms.  Below is modeled precipitation totals from this afternoon's NAM model run for the Northeast through Friday afternoon, with many seeing up to and over 1" and some places seeing 2"+.

18Z NAM model run for precipitation totals through Friday afternoon...courtesy of Tropical Tidbits

 

 

Heat and Humidity Return This Week

    Lately it's almost felt like summer was winding down and fall was right around the corner, as highs dropped to around 80° and into the low- to mid-80's with uncomfortable humidity almost nowhere to be found.  However, that's all changing starting today and for the week ahead as true summer-like conditions ramp back up and soupy air make a return.  Heat is already here to stay, and humid conditions will be on a gradual rise through the beginning of the week, culminating in the threat for scattered showers and storms for the latter half of the week.

   As I said before, high temperatures have already set into the region, but dew points will certainly be on the rise for tomorrow through Tuesday, as shown in the model data below.  We'll continue to see mostly sunny skies dominate the landscape due to a high pressure system over our area.  However, as it slides offshore, flow will come out of the southwest providing for an increase in moisture and retention of heat, so this is where the humidity increase will come from.  Generally speaking, 60-65° starts to feel sticky (tomorrow), 65-69° is uncomfortable (Monday), and 70°+ is oppressive (Tuesday), so we'll be going through all of these stages over the next few days (with highs in the 90's).

GFS MOS Data with dew points highlighted in a red box

    So when will we see rain again?  A June that was 5.65" above normal in rainfall (in Philadelphia) quelled drought concerns, but a below-average July in precipitation has made it seem pretty dry recently (almost in the lowest drought category per The National Drought Mitigation Center).  However, it appears that we could see a showery and stormy end to the week due to an approaching cold front.  Tuesday and Wednesday will see the slight threat for an isolated shower or storm, but those days will more likely than not remain dry, with partly sunny conditions.  This does not quite look to be the case for Thursday and Friday though.

   A low pressure system will move across the Great Lakes/Upper Midwest region on Thursday, and its associated cold front will affect our region to end the work week.  The period from Thursday morning to Friday evening has the highest precipitation threat for the week, with the chance for showers, downpours, and thunderstorms, with breaks of sunshine between.  Below is the GFS model run for this morning displaying Thursday's precipitation to give an idea of the rainfall across the area as the cold front approaches,  As always with being this far out, if this front speeds up, we could be looking at some rain sneaking its way into your Wednesday PM.

12Z GFS model run showing Thursday at 2pm (Image courtesy of Tropical Tidbits)

 

4th of July Weekend Forecast

Rest of Friday
    The rest of the daytime hours will be beautiful, with highs in the 80's and a mix of  clouds and sun.  Clouds will build through the rest of the day, as a low pressure system approaches the west and brings the threat for showers overnight tonight.

Saturday (4th of July!)
    As a low pressure system approaches the area and moves off just to the south, we'll see the threat for showers throughout the day tomorrow.  The best chance for precipitation looks to be during the morning and early afternoon, with chances for rain dwindling as you head into the evening hours.  Highs will likely remain in the upper-70's, with just enough humidity to feel a little uncomfortable but not bad.

This morning's NAM model run showing simulated radar at 11am tomorrow

Sunday
    High pressure builds back in and provides for plenty of sunshine and comfortable conditions.  Highs will jump back up into the mid-80's, making for a great end to the holiday weekend!

Tropical Storm Bill's Remnants to Bring Weekend Rain

    Tropical Storm Bill made landfall along Texas' Gulf Coast on Tuesday, June 16th, with winds to 60 mph and heavy rain.  Now, less than a week later, our area will be affected by the rainy remnants of that tropical cyclone.  Bill has certainly left its mark on the areas that it has passed through, bringing several inches of rain to portions of Texas and Oklahoma and severe weather (including tornadoes) to the Midwest.  Below is a radar loop of what Tropical Depression Bill looked like this evening over the Missouri/Illinois/Kentucky border area.

Tropical Depression Bill Radar Loop (Gif courtesy of RadarScope)

    So how will these tropical remnants affect our Father's Day Weekend in southern New Jersey?  Well, an unstable atmosphere will allow for scattered showers and thunderstorms to spark up across the region on Saturday during the daytime hours.  However, this is not the main concern.  Bill's area of low pressure will approach and push through Philadelphia and South Jersey late Saturday night and into Sunday morning.  The heaviest of the rainfall and storms look like they will fall after midnight and last into Sunday morning (likely out by 9am-12pm).  The image below shows this afternoon's NAM model run of the simulated radar at 8am on Sunday morning, showing heavy precipitation over the area.

18Z NAM model run's for Sunday morning at 8am (Image courtesy of Tropical Tidbits)

    The whole region is under a Flood Watch due to the potential for a long duration of heavy rainfall over a short amount of time.  Generally-speaking, it looks like we will be looking at upward of 1-3" of rain through overnight hours of Saturday/Sunday and Sunday morning.  Though, isolated locations could see 3"+ of rainfall, as the low pressure center brings a ball of very heavy precipitation into Southeast Pennsylvania and New Jersey. The image below shows a swath of heavy rainfall totals through Sunday evening from Kentucky to South Jersey.

Modeled precipitation totals through 8pm on Sunday evening (Image courtesy of the WPC)

    Finally, it does appear that when the rainfall ends Sunday morning, dry air will quickly pull in behind it to begin to dry things out.  Sunshine will likely make a return for the afternoon and evening (partly cloudy skies), but there will be the threat for scattered PM showers and storms as a low moves off to the north and a front moves through the area.

Rain and Storms Possible Through Tuesday Night

  It's looking like a rainy/stormy week ahead, with the threat of rain and storms possible each day.  This threat will especially be there for the next few days through Tuesday night (and again to end the week due to a tropical disturbance currently in the Gulf of Mexico).  Anyway, hot temperatures, humid air, and the chance for rain and storms (some have the chance of being severe) will be interspersed with periods more clouds than sun.  This weather is thanks to the set-up that will feature a warm front over the region through Tuesday evening, when a cold front will push through.

Today
  We'll see partly to mostly cloudy skies, with highs in the mid- to upper-80's.  Humidity levels won't be as bad as they will be in the coming days, and it'll be mainly dry throughout the afternoon and early evening.  Toward 7pm and later, we'll be looking at the threat for showers and storms, with periods of rain possible, especially after nightfall and overnight.  The severe threat won't really be there as much as tomorrow and Tuesday though.  The image below shows this morning's NAM model run simulating the radar for tonight at 11pm depicting moderate to heavy rain and storms over the area.

Above: This morning's NAM model run depicting the radar at 11pm tonight (Courtesy of Tropical Tidbits)

Tomorrow and Tuesday
  This will be the time period to really be on the lookout for thunderstorms and severe weather, as the atmosphere will have more instability.  Tomorrow will feature the chance for rain and storms throughout the day, and some storms could be severe, with the main threats being heavy rain and gusty winds.  Otherwise, dry periods will be under mostly cloudy skies, with highs around 90° and heat indices into the mid- to upper-90's (oppressive humidity).

  Tuesday will see much of the same, except with the threat beginning toward mid-day.  Though severe storms are more likely on Monday, the chance for them will remain for Tuesday, with periods of heavy rain and gusty winds being of main concern.  Highs will be 85-90°, with very oppressive humidity.  The cold front then pushes through during the evening.

Overview
  In general, it looks like most areas will be looking at upward of around 1" of rain through Tuesday; however, isolated areas could be looking at more under repeated downpours and storms, which is the norm during the spring and summer months.  The image below shows modeled rainfall totals through Wednesday at 8am and depicts upward of 1-3" across the area during that time frame.  Finally, threats for rainfall and storms will continue throughout the rest of the week, especially as moisture from what could be Tropical Storm Bill has the chance to affect the area toward the end of the work week.  However, tomorrow and Tuesday remain the best chances for severe thunderstorms.

Above: Modeled rainfall totals between today at 8am and Wednesday at 8am (Courtesy of NOAA)