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Weather Forecasts

WEEKEND WEATHER FORECAST

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Fri 11:30 PM – The two versions of the WRF model just available show showers as early as 1PM Sunday and more sun than the GFS or NAM. High temp 86-88 on Sunday.

The WRF model forecasts have been really impressive lately. The downside is the model comes out late, only forecasts out to 48 hours and is only run twice daily. But accuracy is worth the wait.  

Fri 10:45 PM – Tonight’s NAM has more sun, less cloudiness on Saturday afternoon, more clouds on Sunday.

Saturday will begin with the incredibly nice weather we had today (Friday).

As the crisp, unseasonable airmass over us moves off to the east, weak low pressure from the Midwest will pass to our north on Sunday. A southwesterly flow of increasingly humid and unstable air will move in for Sunday.

Saturday will start sunny and delightful.  High temperature 82-84. During the afternoon a very weak “pseudo warm front” will approach.  An increase in cloudiness expected with mostly cloudy skies by late afternoon.

Sunday will be mostly cloudy (some bright spots possible), warm and increasingly humid. As the warm front slowly moves to our north Sunday, light showers  are possible in the morning, mostly far north and west, although a sprinkle or quick shower can’t be ruled out here.  With increasing heat and humidity and an upper air disturbance moving through, expect showers and thunderstorms to break out in the afternoon.

The FV3-GFS I spoke of earlier this week has fully replaced the older GFS. The “FV3-GFS” after this past Wednesday IS the “GFS” now.

The GFS has the chance of light showers as early as 1 PM.  Most of the shower and thunderstorm activity is expected during the late afternoon and evening hours according to both the NAM and GFS.

I’ll update over the weekend to give a more specific timing and indicate whether some areas will have any severe weather.

What’s with this cool weather? Remember, we’re just coming off the 10 year sunspot cycle minimum. Back in the summer of 2009, we had fewer days in the 90s and many similar very cool spells. I’ve talked about this in the past.
Weather Forecasts

WEEKEND WEATHER FORECAST

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Sat 8 AM : Sunday forecast uncertainty:  Last night’s model runs show differences between the NAM (cloudy, cooler and windy High low to mid 70s) and the FV3-GFS (A mix of sun and clouds, breezy warm.  High near 80. ) Will need to wait for today’s models to have a better handle on Sunday’s weather.
Fri 11 pm: Tonight’s NAM shows considerable cloudiness again for Sunday afternoon. Reduced high temp on Saturday to 81.

Periods of high, thin cloudiness (cirrostratus) will be with us over the weekend, as this moisture high in the atmosphere (34,000 ft) is all that will be able to move towards us from the south.   Rain in the Carolinas will be suppressed to our south, as high pressure builds over our area from the northwest, keeping us dry.

Saturday will be similar to today (Friday).  Periods of sun and high thin cloudiness.  High temperature 84 (EKDMOS) or 81 (NBM model).

Sunday is looking better than it did earlier.  While it appeared that there would be more clouds than Saturday, things have changed with today’s models.  Periods of sun and high clouds. it appears now that there should be more sun than Saturday! No rain expected.  High 81 (NBM) or 78 (EKDMOS model).

FV3-GFS Model- Composite Cloud layers (shading)  for 3 PM Sunday. Philadelphia is in the clear!

 

Weather Forecasts

WEEKEND WEATHER FORECAST

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The forecast for the weekend has already changed a bit from my “forecast outlook” of yesterday.

Low pressure that moved to our south today (Friday) had brought some unexpected cloudiness at times during Friday afternoon.

This low pressure system is expected to consolidate off the coast and will result in a general easterly flow on Saturday, keeping temperatures a bit cooler than previously forecast as a result of cloud cover, especially in NJ.

While tonight’s major models are not yet available, the short range models just available show a fair amount of cloudiness during the morning and early afternoon on Saturday. The GFS was showing a high 87-89, but the NAM and latest short range models show much lower highs of 81-84.

11 PM Tonight’s NAM has much more sunshine on Saturday than the earlier short range models.

A weak wave ahead of an approaching cold front moves through around midnight Saturday with some showers and possible thunderstorms, although the latest trends show the showers falling apart before arriving in Philadelphia.

For Sunday, a cold front will approach during the day, ahead of a significant amplification in the jet stream.  Mostly sunny early with cloudiness moving in during the early to mid afternoon.  Current models show showers and thunderstorms about 3-6 PM Sunday.   High 80-84.

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MEMORIAL DAY WEEKEND WEATHER FORECAST

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As discussed in yesterday’s Weekend Outlook, our weather this weekend will be influenced by an strong upper air high pressure centered over Georgia and Alabama. Areas of vorticity will rotate into our area around this upper level high.

The weekend’s weather will depend on the timing of these impulses and the models have been consistent in having the these disturbances affect us during the night time hours of both Saturday and Sunday.

It should be noted that at the time of this post, none of the models are predicting the showers in the northwest corner of Pennsylvania that are occurring now. The confidence level of this forecast is a bit below average.
WRF Model Depiction of Areas of Vorticity around 18,000 feet 1 PM Saturday with their direction of movement (red arrows)

Saturday will have a mix of sun and clouds.  High 78-80.  Cloudiness will be more prominent north and west of the city, less at the shore.  (The models differ in the amount of cloudiness.)  A south-southeasterly flow of moisture ahead of these disturbances will cause the cloudiness to thicken later in the day on Saturday.

The vorticity will drag a warm front over our area Saturday night. Light showers possible Saturday night; most of the rain far north and west of Philadelphia.

Sunday:   After some early morning clouds, Sunday will become mostly sunny and very warm.  High 88-90.

However, another upper air disturbance approaches from the northwest  with increasing  cloudiness on Sunday afternoon.  It will drag a cool front through our area Sunday night.

Showers develop late in the day or the evening Sunday, again mostly far north and west of the city.  (The models differ in the amount of precipitation- the GFS keeps us dry, the NAM has showers.)

A northwesterly flow of drier, somewhat cooler air in store for Monday.

Monday: After some early clouds, Monday will become mostly sunny and pleasant. High 84-86.

Friday Afternoon’s GFS has much more cloudiness on Monday than the NAM. Will need to update over the weekend.