Monthly Archives: March 2020

Weather Updates

WEATHER UPDATE FOR FRIDAY

[su_note note_color=”#defcdc”]The mystery of why the models are showing rain instead of snow has been solved.  The models are forecasting a layer of warm air in the lowest 1500 feet of the atmosphere.[/su_note]

The Friday storm discussed earlier this week still remains a forecast challenge.  Let me start by saying that ALL models currently forecast rain, not snow, for our area because near surface temperatures are expected to be well above freezing.

That said, there are many model parameters that historically predict snow for us and many features that still need to watched.

Basically a low pressure system was expected to come together and phase with an upper low resulting in an intense coastal storm.   That scenario has faded, as phasing is expected to occur later, out in the Atlantic.

Here’s the current GEFS (Statistical Ensemble) mean forecast for Friday at 12 PM:

GEFS 12 PM Friday forecast  Blue Arrow points to upper low and the black arrow to the surface low.

Below is the current SREF (Short Range Ensemble) forecast, showing a somewhat similar position of the surface low, but with this forecast, I have drawn in the snow-critical temperature lines.  Notice that we are on the north side of these critical temperatures, usually meaning snow for us.

SREF 12 PM with critical snow thickness.  We are north of these critical snow temperatures, usually meaning snow for us.

I’m sure the models ‘know what they’re doing’ regarding snow forecasting, but with this complex upper-low/surface low combination, it will be interesting to see what actually happens.

What I expect is for some snow to mix in with the rain especially later in the day, but no accumulation.  Let’s see what happens.

 

Philadelphia Weather Outlook

WEATHER OUTLOOK UPDATE

[su_note note_color=”#defcdc”]Update Tue 09:01 AM —Cancel that Friday storm!

Last night’s models totally moved away from predicting a highly phased storm along the coast for Friday.  Wow, what a change in forecast! Most of the rain will move much further south without jet stream phasing.

So I think that’s probably it with any snow this winter.  [/su_note]

Well, there hasn’t been much ‘weather action’ here this winter.  However, this coming Friday might be the last possibility for any winter weather this year.

There’s much uncertainty about the nor’easter that’s expected to develop in the western Atlantic, but the trend has been for a deep and jet stream phased storm that comes closer to the coast. All models have some form of precipitation, mostly rain for our area.

However, thermal profiles suggest that while we might not get much, if any accumulation, the precipitation may fall as wet snow Friday afternoon.   Basically, the temperatures near the surface are expected to be above freezing, but this highly dynamic system with a closed upper low will have cold air at critical levels for snow to form.

Here is the current GFS forecast for Friday afternoon—

GFS Forecast Friday afternoon

Here’s the current Canadian GDPS  forecast—

Canadian (CMC) Global Deterministic Prediction System Model (GDPS)

It just bears watching.  Sometimes these storms seem to come out of nowhere this time of year, when in fact, the models are suggesting something interesting in this time frame.  Stay tuned.

 

Philadelphia Weather Outlook

WEEK WEATHER OUTLOOK

We’ve gotten through February with virtually no snow.

As mentioned with my “Weather Outlooks” on February 12th and again on February 18th, the weather pattern of the past few months has been highly predictable and consistent, but changes are in the pattern are inevitable and usually come around just before the change in seasons.

“The current pattern has been with us for almost three months. Like bull stock markets, weather patterns don’t last indefinitely. Weather patterns tend to change as the seasons change.”

Back on February 18th, I saw large increases in the “spread” of the statistical members of the EKDMOS for the last week in February and the first week in March, suggesting a weather pattern change might be on tap.

Well, we’re here in March and indeed, a pattern change is being discussed by the NWS Extended Weather Forecasters Group.

Specifically there are now large spreads and differences in the extended statistical  models and there are hints of a deep storm  forming in the western Atlantic which may bring some interesting weather for us around this Friday’s time frame.  (Hey, it’s the Philadelphia Flower Show week and how many years has some portion of the show been plagued by bad weather forecasts!)

Here’s the current Canadian GEM (GDPS) forecast for Friday morning—

Canadian GDPS forecast for 10 AM Friday

A little far offshore, but this should watched.  I’ll keep an eye on this.