SPC 0830Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0140 AM CST Sun Feb 21 2021

Valid 231200Z - 241200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for thunderstorms appears negligible across the U.S.,
Tuesday through Tuesday night.

...Discussion...
The area of lowest mid-level heights over the Arctic, initially to
the north of Alaska and the Canadian Yukon and Northwest
Territories, may slowly begin to shift east-southeastward during
this period.  Otherwise, models indicate that a fairly prominent,
blocking mid-level ridge will persist across the southern
mid-latitude eastern Pacific.  

Within the stronger, broadly anticyclonic westerlies between these
two features, a number of short wave troughs will remain progressive
across the northeastern Pacific into British Columbia and the
Pacific Northwest.  In association with the perturbations
progressing inland, it appears that flow will trend broadly cyclonic
across the Intermountain West into the Mississippi Valley, while
downstream flow trends broadly anticyclonic into the northern and
mid Atlantic Seaboard, in the wake of large-scale troughing rapidly
progressing offshore into the western Atlantic.

These developments will be accompanied by further low-level cooling
and drying across the northeastern Gulf of Mexico and the south
Atlantic Seaboard, including the Florida Peninsula.  Although a
southerly return flow may develop across the western Gulf of Mexico
into the northwest Gulf coast region, it still appears that
low-level moistening will be quite modest due to slow boundary-layer
recovery in the wake of the recent Arctic intrusion.

...Northern Rockies vicinity...
Insolation beneath the western periphery of a broad pocket of cold
mid-level air (including -35 to -40C around 500 mb) may contribute
to weak boundary-layer based CAPE and scattered convective
development Tuesday afternoon, although thermodynamic profiles
probably will be mostly below freezing.  It might not be out of the
question that some of this activity could become capable of
producing lightning, but it seems mostly likely that any such
occurrences will be sparse in coverage and short-lived, and
thunderstorm probabilities appear less than 10 percent.

...South Florida...
Prior to the passage of the cold front, there appears some risk for
isolated thunderstorm development near southeast coastal areas,
though probabilities exceeding 10 percent may be mostly over the
coastal waters.

..Kerr.. 02/21/2021

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