Prognostic Meteorological Discussion
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FXUS21 KWNC 201850
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 20 2019

SYNOPSIS: The Week-2 weather pattern is expected to feature fairly persistent
upper-level low pressure over the western CONUS, upper-level high pressure over
the eastern CONUS, and unsettled weather throughout the middle CONUS. Below
average temperatures are expected in the northern Rockies and the season`s
first heat wave is expected throughout the Southeast. There will also be
several opportunities for significant rainfall throughout the Plains and
Mississippi Valley, although there is still too much uncertainty to pinpoint
exactly where and when. Although we expect fairly active weather throughout the
Gulf of Alaska, there are no hazards forecast for the state.

HAZARDS

Slight risk of much below normal temperatures across parts of the western third
of the CONUS, Tue-Wed, May 28-29.

High risk of excessive heat across parts of the Southeast, Tue-Thu, May 28-30.

Moderate risk of excessive heat across parts of the Southeast, Tue-Mon, May
28-Jun 3.

Slight risk of excessive heat across parts of the Mid-Atlantic and Southeast,
south and east of the Appalachians, Tue-Mon, May 28-Jun 3.

Moderate risk of heavy precipitation across parts of the Central and Southern
Plains, and Middle and Lower Mississippi Valley, Tue-Wed, May 28-29.

Slight risk of heavy precipitation across parts of the Central and Southern
Plains, and the Mississippi Valley, Tue-Mon, May 28-Jun 3.

DETAILED SUMMARY

FOR THURSDAY MAY 23 - MONDAY MAY 27:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR TUESDAY MAY 28 - MONDAY JUNE 03: The Week-2 synoptic pattern over North
America is forecast to be characterized by troughing over the West and ridging
over the East. Generally unsettled weather is expected throughout the core of
the upper-level geopotential height gradient over the Central and Southern
Plains and Mississippi Valley.



Troughing over the western CONUS is expected to lead to below normal
temperatures throughout the northern Rockies and there is a slight risk of
below normal minimum temperatures posted for May 28-29. Minimum temperatures on
these days could be below freezing.



Synoptic-scale ridging centered over the Southeast will bring the first heat
wave of the season to the region. There is a slight risk for excessive heat
over most of the Southeast, south and east of the Appalachians. There are also
areas of higher confidence embedded within that region where the model
agreement is strongest. Maximum daily temperatures within this area are likely
to be in the 90s and low 100s throughout the entire forecast period. The GEFS
moves the heat out by May 30, whereas the ECMWF maintains the heat for the
entire forecast period. The regions of moderate (40%) and high risk (60%) for
excessive heat, centered over southern AL, GA, coastal SC, and northern FL,
reflect the areas in which the models agree most. Daily high temperatures in
these areas are likely to be near or above 100F during the first three days of
the period, and then in the mid-90s for the remainder of the period if the
ECMWF model`s solution is correct. We expect this to be a relatively dry heat -
both the GFS and ECMWF ensembles are forecasting below-average dew points
during the event, which will keep heat index values close to their dry-bulb
counterparts.



The strongest geopotential height gradient is expected to set up over the
Plains and Mississippi Valley, which will in turn lead to the most active
weather in the CONUS. Both the GFS and ECMWF ensembles suggest that fairly
persistent low pressure over that area will lead to several opportunities for
rain, which is represented by a broad slight risk (20% probability) hazard.
It`s difficult to pinpoint exactly where and when the heaviest rain will occur,
but models suggest that a couple of events with daily rainfall of 2-3 inches
are likely during the forecast period. The highest probabilities (~40%) of
hazardous rainfall amounts greater than 1 inch/day are around the
OK-KS-AR-MO-IL area on May 28-29.



FORECASTER: Kyle MacRitchie

$$




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