Updated Tue 8:30 AM : The trend continues towards a westward track off the NJ coast, and a merging with a Great Lakes low and associated cold front . The remnants of Elsa are not forecast to be very strong. Just a moisture source for additional rain. Some models have the associated rain east of the storm with little effect here.
What could be more conditional than an if-else (Elsa) storm situation!
I’ve been following the path of Elsa, as forecast by the GFS, GEFS, Canadian GDPS, the ICON Global and the NBM.
The models have been showing a significantly more westward track for Elsa over the past 24 hours, bringing it closer to the NJ coastline and the Philadelphia area in the late Thursday through Friday time frame.
After several hot days Tuesday and Wednesday, an approaching cold front will bring thunderstorms as early as Wednesday evening and Thursday.
The speed of the cold front will affect the path of Elsa in our region. If the cold front slows down, we will have much more rain and wind.
The latest GFS model has several inches of rain possible this week for the Philadelphia area and eastward, but the NBM rainfall amounts are not impressive right now.
Here’s the current GFS model forecast for 7 PM Thursday—
GFS model forecast (simulated radar, cloud cover) for 7 PM Thursday. This represents a significant change over the past day to a more westward track . (Click on image for a larger view.)
These tropical storm forecasts always to change over time. Stay tuned.
Sun 06:50 PM Forecast Review — Sunday’s showers is a perfect example of why I began this blog post from Friday with
“exact forecasts with an upper closed low are fraught with difficulties, inaccuracies and uncertainties.”
A mid-levelupper air disturbance rotating around the upper low, unpredicted by most of the earlier models today, caused the scattered showers Sunday afternoon. I don’t think weather models, as good as they can be, can do any better with forecasts and upper air closed lows.
Looking back at this morning’s models, the HIRESW-ARW2 did predict the showers, but it didn’t become available until after 10:20 AM. Had I actually looked at the HIRESW-ARW2, I don’t think I would have updated my forecast; there were too many models not showing showers.
Our weather early this weekend will be affected by a cyclonic flow of air around an upper closed low pressure system. This flow and the upper closed low pressure system’s cold air aloft results in instability clouds and showers.
As my regular readers know, exact forecasts with an upper closed low are fraught with difficulties, inaccuracies and uncertainties. Such may be the case this Saturday. The upper low’s effects are expected to diminish by Sunday.
(Today, Friday, is a perfect example. Some areas are having showers and some areas have sun breaking through clouds. This morning’s models have been unable to pinpoint the proper timing and placement. )
I’ve compared current radar with six different models run this morning. The HREF has had the highest skill in the forecast location of the current rain this afternoon. So I’m going to lean on that model for Saturday.
Here’s the current HREF forecast for Saturday at 1 PM (there’s a chance of showers in many areas) —
HREF forecast for 1 PM Saturday showing rain (bright green contours) and clouds (blue shading) Upper low center (L) Arrows show upper air cyclonic counterclockwise circulation around upper low. (Click on image for a larger view.)
So, it looks like considerable clouds and showers develop Saturday afternoon. It won’t be raining all afternoon.
The upper low moves away on Sunday and Monday, but still a low chance of showers Sunday late afternoon.
NBM – 1 Hour Rain Probability meteogram, Blue Bell. Anything over 15% probability for a 1 hour period is a good chance. (Click on image for a larger view.)
Considerable cloudiness, perhaps some sunny breaks at times with scattered showers, especially in the afternoon. Breezy. High 73.2 ± 3.2º (NBM Blue Bell) Update:Tonight’s models have reduced the showers Saturday afternoon. Following morning clouds, look for considerable sunshine in the afternoon, except far western suburbs.
Sat Morning Update: Despite my optimistic update from last night, the early morning model runs (06z) have reverted back to the original forecast of plenty of showers developing throughout the day, especially late afternoon.
NBM 1 hour rain forecast Saturday 3 PM—
NBM Saturday 3 PM – 1 hour rain and cloud (dark shading) (Click on image for a larger view.)
The upper low moves off. Some cloudiness in the morning, breaking way to a mix of sun and occasional clouds. A chance of a shower late afternoon. . High temp 78.4 ± 2.1º NBM Blue Bell
Sunny and warmer. Some models show widely scattered showers between noon and 3 PM, although this may be model noise. High 86.0º ± 3.1º (high spread!).High 87.6º ± 1.6º NBM Blue Bell.
