Prognostic Meteorological Discussion
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FXUS02 KWBC 312057

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
456 PM EDT Tue Mar 31 2020

Valid 12Z Fri Apr 03 2020 - 12Z Tue Apr 07 2020

...Overview and Guidance/Predictability Assessment...

Guidance generally shows varying degrees of mean ridging from the
northwestern Caribbean/Gulf of Mexico through much of eastern
North America into northern Canada, while upper troughing prevails
over the western part of the continent/West Coast.  Flow around
the south side of a broad upper low initially over western Canada
will cross the northern tier states, bringing a front into the
East.  One Pacific impulse should reach near the West Coast around
early Sat and quickly eject inland, followed by a deeper and
slower system by Sun-Mon.

Guidance agrees fairly well for significant features during days
3-4 Fri-Sat, allowing for an operational model blend to represent
consensus well.  Day 5 Sun exhibits some spread/trending for the
trough and possible embedded upper low nearing the West Coast.
Through the 00Z/06Z cycles the CMC/UKMET tracked the upper low
somewhat farther offshore than other solutions, while the majority
cluster has adjusted the core of the trough a bit southward.
Ultimately the multi-model blend was good for depicting this
southward trend while leaning away from the 00Z CMC/UKMET
specifics.  Note that through Sun the new 12Z CMC/UKMET are closer
to the consensus while the 12Z GFS has trended south of previous
runs.  In contrast, the new 12Z ECMWF carries the core of the
upper trough north of its 00Z run.

The ultimate progression of this feature after early Sun depends
upon its exact path up to that point and then influence from
increasingly uncertain upstream flow over the northeastern
Pacific.  Differences among individual ensemble members as well as
consecutive operational model runs from the past couple days
highlight the low confidence in northeastern Pacific details.
Based on data through the 06Z cycle, preferred to side with the
06Z GEFS/00Z ECMWF means and 00Z ECMWF which were in the middle of
the spread for trough progression.  The 00Z/06Z GFS became quite
fast to eject the trough into the Plains while the latest CMC runs
stray to the slow side of the spread (albeit not much slower than
the new 12Z GEFS mean).  The 12Z GFS shows a favorable trend,
slower than the 06Z run by 12-24 hours by next Tue.

...Weather/Hazard Highlights...

Expect a large portion of the West to see at least some rain and
high elevation snow during the Fri-Tue period, with the Desert
Southwest and southern Rockies having the best possibility of
staying mostly dry.  The first Pacific system will be fairly
compact and bring the best precipitation focus to northern
California and vicinity with some moisture extending to the
northern Rockies.  The second system will likely bring highest
totals to northern California/Sierra Nevada and spread a larger
shield of precipitation across the West, possibly as far south as
the coastal ranges of southern California.  Depending on exact
tracks of these systems, southwestern Oregon could receive
significant precip as well.

A front pushing across the Plains and east-central U.S. late this
week/early weekend will focus an axis of mostly rainfall,
including the potential for some locally heavy activity over and
possibly east of Texas.  Sufficiently cold air may exist to
promote some snow over Minnesota/extreme northwest Wisconsin
around Fri.  With time expect the precipitation along the front to
become lighter and more scattered especially across northern parts
of the East.  Another area of rainfall may develop across the
eastern half of the country late weekend into next week with the
best signal for some significant totals extending from the
Southern Plains into the Tennessee Valley.  Other areas could see
enhanced activity as well but with lower confidence.

Cold air behind the late week Plains/Mississippi Valley front will
bring temperature anomalies down to 10-25F below normal over the
northern-central Rockies/Plains on Fri, followed by a warming
trend.  The overall pattern aloft will tend to favor moderately
below normal readings west of the Rockies during the period.
Minus 5-10F or so anomalies for highs should be most common over
California/Nevada early next week.  On the other hand above normal
temperatures will become more expansive to the east of the
Rockies.  By next Mon-Tue expect broad coverage of at least plus
10-20F anomalies, with morning lows tending to be somewhat more
extreme versus normal than the daytime highs.


Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:

- Heavy rain across portions of the Southern Plains, Tue-Wed, Mar
3-Mar 4.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Wed-Thu, Mar
4-Mar 5.
- Heavy snow across portions of the Central Great Basin,
California, and the Southwest, Sat-Tue,
Apr 4-Apr 7.
- Flooding possible across portions of the Middle Mississippi
Valley, the Great Lakes, the Upper
Mississippi Valley, and the Northern Plains.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Northern
Plains, the Tennessee Valley, the Middle Mississippi Valley, the
Upper Mississippi Valley, the
Southern Plains, and the Ohio Valley.
- Flooding likely across portions of the Great Lakes, the Middle
Mississippi Valley, the Southern
Plains, the Upper Mississippi Valley, and the Northern Plains.
- Much below normal temperatures across portions of the Central
Plains, the Northern Plains, and
the Northern Rockies, Fri, Apr 3.

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

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