Prognostic Meteorological Discussion
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000
FXUS21 KWNC 171942
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 17 2019

SYNOPSIS: Mid-level high pressure is anticipated to dominate the western half
of the Contiguous U.S. during Week-2, supporting above-normal temperatures
across the western third of the country. A stalled front across the Southeast
and Texas may bring above normal precipitation to the Gulf Coast states and
coastal parts of the Mid-Atlantic during the period. Some models indicate the
potential for a series of surface low pressure systems across mainland Alaska
and the Bering Sea during Week-2, supporting anomalously high wind speeds
across parts of western and southern Alaska. Additionally, mid-level high
pressure is anticipated across much of mainland Alaska, favoring anomalously
warm temperatures across the state. These warm temperatures and windy
conditions may prolong wildfire risk across parts of Alaska during Week-2.

HAZARDS

Moderate risk of excessive heat for portions of California, Thu-Sun, Jul 25-Jul
28.

Slight risk of excessive heat for portions of the western third of the CONUS,
Thu-Tue, Jul 25-Jul 30.

Slight risk of heavy precipitation for portions of Florida, Thu-Mon, Jul 25-Jul
29.

Flooding possible across portions of the Four Corners region, Thu-Sat, Jul
25-Jul 27.

Slight risk of much above normal temperatures for portions of the Alaska
Panhandle, mainland Alaska, and the Aleutians, Thu-Tue, Jul 25-Jul 30.

Slight risk of high winds for portions of mainland Alaska, Thu-Mon, Jul 25-Jul
29.

DETAILED SUMMARY

FOR SATURDAY JULY 20 - WEDNESDAY JULY 24:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY JULY 25 - WEDNESDAY JULY 31: Amplified mid-level high pressure is
forecast to dominate the western half of the CONUS throughout Week-2. A broad
area is highlighted for a slight risk of excessive heat across the western
third of the CONUS, July 25 to 30. The GEFS reforecast tool indicates a much
more widespread area of >20% chance of reaching the 85th percentile compared to
the ECMWF reforecast tool, which maintains most of the heat to California and
the Southwest. Given the potential that there is a possibility of this being a
multi-day heat event, a larger spatial area is highlighted. The reforecast
tools show some areas reaching the or exceeding the 90th percentile. A moderate
risk of excessive heat is posted for California July 25 to 28, given the good
model agreement today and good run to run consistency in the ECMWF the last few
days regarding this hazard.



The positioning of the mid-level ridge across the western CONUS may continue
the increased likelihood of precipitation across the Four Corners region during
Week-2. There is good agreement between the GEFS and ECMWF reforecast tools
indicating a >20% chance of some areas receiving up to half an inch of rainfall
in a 3-day period. A possible flooding hazard is highlighted across the Four
Corners where localized convection and flash flooding are possible.



Amplified mid-level troughing is predicted across the eastern half of the CONUS
throughout Week-2. This troughing may sink as far south as the Southeast and
Lower Mississippi Valley. A stalled front ahead of this trough in conjunction
with ample onshore moisture associated with a subtropical ridge over the
western Atlantic Ocean increases the likelihood for rainfall across the Gulf
Coast states. A slight risk of heavy precipitation (>20% chance of 3-day totals
reaching or exceeding the 85th percentile and one inch) is posted for parts of
Florida, July 25 to 27. Parts of the Gulf Coast states may receive an inch or
greater of rainfall in 3-days associated with this front. However, since these
totals are around the 80th percentile, a heavy precipitation risk is not
highlighted since it does not reach the 85th percentile threshold.



A series of surface lows are anticipated to form over the Bering Sea and
mainland Alaska during Week-2. This pattern favors an enhanced likelihood of
high winds across parts of Alaska. A slight risk of high winds is highlighted
across parts of western Alaska, coastal northern Alaska, and the Alaska
peninsula, July 25 to 30. There is a potential for amplified ridging across
parts of mainland Alaska during Week-2. Both the GEFS and ECMWF reforecast
tools are in good agreement regarding widespread >20% chances of maximum
temperatures reaching or exceeding the 85th to 90th percentile compared to the
GEFS reforecast tool. A broad area of slight risk of much above normal
temperatures is posted across parts of mainland Alaska, July 25 to 29.
Increased risk of high winds and much above normal temperatures may continue
the risk of wildfires across parts of Alaska. According to the Alaska
Interagency Coordination Center, over 1.64 million acres have burned statewide
(as of July 17th, 2019) since the beginning of the year.

FORECASTER: Melissa Ou

$$




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