FRIDAY FORECAST

[su_note note_color=”#ffffff”]Updated Fri 09:07 AM — Consistent with the poor performance forecasting this system, the models have moved the time of showers to this morning instead of noon – 3 PM.

So the latest attempt at an [accurate] forecast is light scattered showers this morning, occasional sun through thinning clouds this afternoon.  Another chance of scattered light sprinkles late afternoon.  High 65.2º sd 1.6º.  [/su_note]

So, the winds were impressive today but the amount of rain was less than the models had originally forecast.  The onset timing and structure of the storms were progressively different than had been modeled.

The storms expected after midnight tonight are no longer forecast by tonight’s models.

Tonight’s models show the location of the surface low not to be directly over us on Friday as had been originally forecast. As a result, the location or occurrence of showers Friday is low confidence.

Weather forecasting is a very tough business. Today’s forecast models, which I followed closer than usual, have over the day transitioned to a scenario that is remarkably different than it was 12 hours ago.

So here’s tomorrow’s somewhat low confidence forecast– partly sunny, some clouds late morning and early afternoon.. A chance of showers about noon to 3 PM.  High 66.3 sd 3.5° Increasingly windy towards evening.

Brief Update:  The 2 PM (18z) model runs are coming in.  Here are the trends—

The storm can best be seen as coming in three parts:

Heavy rain starts 5-6 PM (Blue Bell) and moves out quicker than previously forecast.  High winds peak about 8PM.   Rain tapers off after 9-10 PM.  QPF is down to about 1 inch

Isolated, possibly heavy, thunderstorms again between midnight and 3 AM.

On Friday, upper low combines with surface low pressure over us.   Additional heavy rain/thunderstorms morning and early afternoon.  Additional 1 inch of rain possible  Less wind.

Brief Update: Latest NAM-NEST and HRRR not appreciably changed.  Total precipitation (QPF) about 1.25-2.00 inches.  First line of storms moves in between 3 -5 PM. Below is NAM-NEST Simulated Radar forecast for 4:30PM

This morning’s NAM-NEST 4:30 PM Simulated Radar                (click on image for larger view)

Some of the severe weather parameters have decreased since earlier, and it appears that most of the severe weather most likely in central Pennsylvania.

However, this area of energy may arrive partially intact between midnight and 3 AM, with isolated severe thunderstorms.

So there’s three parts to this weather event:

  1. Main area of heavy rain and wind late this afternoon into evening.
  2. Isolated severe storms after midnight.
  3. Additional showers and thunderstorms Friday morning and afternoon.

A brief update.   The first of this morning’s models are coming in.  Like last night, the trend is for the main area of heavy rain to move in a bit later— between 4:30 and 6 PM.   Winds will be increasing.

The other trend is for less severe storm parameters. “Vertical shear” has reduced with this model run from the extreme values forecast yesterday.

The scattered showers we’re having in the morning now were predicted and won’t last.

HRRR (High Resolution Rapid Refresh) 8AM Simulated Radar Forecast for 4:30 PM—

HRRR 4:30 PM Simulated Radar Forecast  (Click image for larger view)

I’ll update after noon, after reviewing more data.  Stay tuned.