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Valid Monday July 16, 2018 to Friday July 27, 2018
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT July 13 2018Synopsis
: Broad mid-level high pressure is
initially forecast across the lower-48 states during the outlook period, that
is anticipated to transition towards high pressure over the West and low
pressure over the Great Lakes which is maintained through Week-2. At the
surface, a cold front is forecast to stretch from the Great Lakes to the
Central Plains at the beginning of the period and move southeastward throughout
the 3 to 7 day period. Another cold front is predicted to enter the Pacific
Northwest and Northern Plains by the middle of the 3 to 7 day period. Surface
high pressure is forecast across the Western Slope of Colorado throughout the
period, which may help pump heat and moisture into the West. Elsewhere, a
surface low is forecast to shift from the Bering Sea into the Gulf of Alaska
and linger throughout Week-1. Hazards
Detailed Summary For Monday July 16 - Friday July 20:
- Heavy rain across
portions of the Southern Appalachians, the Central Appalachians, the Ohio
Valley, the Mid-Atlantic, the Northeast, and the Tennessee Valley, Mon-Tue, Jul
- Heavy rain across coastal portions of the Carolinas, Wed-Thu, Jul 18-Jul 19.
- Excessive heat across portions of the Northeast and the Great Lakes, Mon,
- Excessive heat across portions of the Central Plains, the Lower Mississippi
Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, the
Southern Plains, and the Ohio Valley, Mon-Wed, Jul 16-Jul 18.
- Excessive heat across portions of California, the Central Great Basin, the
Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Thu,
Jul 16-Jul 19.
- Excessive heat across portions of the Desert Southwest, Fri, Jul 20.
- Heavy rain across portions of the Four Corners Region and Central Plains,
Mon-Tue, Jul 16-Jul 17.
- Heavy rain across parts of northwestern mainland Alaska, Thu, Jul 19.
- Slight risk of excessive heat for portions of California, the Central Great
Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great
Basin, Sat-Wed, Jul 21-Jul 25.
- Slight risk of excessive heat for portions of the Desert Southwest,
Sat-Tue, Jul 21-Jul 24.
- Moderate risk of excessive heat for portions of the Desert Southwest,
Sun-Mon, Jul 22-Jul 23.
- Slight risk of excessive heat for portions of the Southern Plains, Sat-Fri,
Jul 21-Jul 27.
- Moderate risk of excessive heat for portions of the Southern Plains,
Sat-Mon, Jul 21-Jul 23.
- Flooding possible across portions of the Central and Southern Plains, the
Central and Southern Rockies, the Central Great Basin, and the Southwest.
- Flooding possible across portions of the Middle Mississippi Valley and the
Upper Mississippi Valley.
- Flooding occurring or imminent across portions of the Upper Mississippi
Valley and the Northern Plains.
- Severe Drought across the Central Plains, the Central Rockies, the Lower
Mississippi Valley, the Central Great Basin, the Northern Great Basin, the
Southern Rockies, the Middle Mississippi Valley, California, the Southern
Plains, and the Southwest.
A cold front is
forecast to stretch from the Great Lakes to the Central Plains at the beginning
of the period and move southeastward throughout the 3 to 7 day period. This
cold front is likely to bring wet weather to parts of the eastern half of the
CONUS, with the best chances of heavy rain (exceeding 1 inch in 24 hours)
across portions of portions of the Southern Appalachians, the Central
Appalachians, the Ohio Valley, the Mid-Atlantic, the Northeast, and the
Tennessee Valley, July 16 to 17, as well as coastal parts of the Carolinas Jul
18 to 19.
A small region of excessive heat is possible across interior portions of
the Northeast on the 16th, aided by enhanced southerly flow in advance of the
passing cold front. Daily high temperatures in the low 90s are forecast across
upstate New York, Vermont, and New Hampshire with this event, with these values
having been previously shown to drive an increase in heat-health issues and
hospital admissions for the region.
As the cold front boundary moves to the Ohio River, warm and moist
conditions are forecast to its South, along and to the West of the 500-hPa
high. Excessive heat is forecast for portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the
Southeast, the Southern Plains, and the Ohio Valley, on the 16th through 18th
due to the Gulf moisture overspreading the already warm conditions. Widespread
heat index values of 105 degrees F (heat advisory criteria for much of the
region) or more are anticipated, with values above 115 degrees F possible in
some places in the Lower Mississippi Valley and Southern Plains. The northern
periphery of heat across the Middle Mississippi and Ohio Valleys is expected
mainly for July 16, with overnight lows likely to only drop into the upper 70s.
The cold front is forecast to approach this region on the 17th, helping to
limit the duration of the heat event. Parts of Virginia, the Carolinas, and
Georgia may experience heat index values of 105 Deg F and greater Jul 16 to 17.
However, an excessive heat area is not specified over this region since these
heat index values are not as uncommon and are expected to be relatively brief.
Given the oppressive heat in the forecast for these regions, outdoor activities
are advised to be avoided if possible during peak daytime heating. It is in the
best interest of those needing to be outside in the heat to take frequent
breaks, seek shady areas, and pay close attention to their hydration levels.
Persistent 500-hPa ridging with above-normal heights over the Western U.S.
is forecast throughout the outlook period. This scenario is supportive of
continued excessive heat for much of California, the Central Great Basin, the
Pacific Northwest, the Northern Rockies, and the Northern Great Basin July 16
to 19, as the cold front dropping through the Plains is forecast to be unable
to make it west of the Rockies. Here, daily high temperature anomalies of +12
to +16 Deg F are forecast, helping to drive many lower elevation areas to the
upper-90s or potentially triple digits. No record temperatures currently appear
likely to fall with this event for the region, despite the anomalous warmth.
Amplified mid-level ridging may support excessive heat across parts of the
Desert Southwest, July 20. Maximum heat values in this area may reach 110 Deg F
The North American Monsoon appears likely to remain active during Week-1.
Heavy rain (exceeding 1 inch in 24 hours) is forecast across the Four Corners
Region and Central Plains July 16th through 17th as a surge of moisture from
the Gulf of California lifts northward into the region. Flash flooding is also
possible with these monsoonal rains for much of the Four Corners region in
areas that see persistent rainfall or lie downstream of complex terrain
receiving such rainfall. The flooding risk is also extended into the Front
Range of Colorado where low-level easterly, upslope flow could yield flooding
concerns behind the cold front. Those planning outdoor activities where flash
flooding is possible are advised to consider their routes given the elevated
flooding risks. Those encountering flood waters on foot or in vehicles are
advised to avoid entering them, given six inches of water can carry away an
adult while 1-2 feet of water is typically sufficient to sweep away vehicles.
An active pattern is expected for nothern Alaska. Elswhere, a relatively
cool, quiet period appears to be in store across Alaska during much of Week-1.
Surface low pressure is forecast to develop along a stationary front across
northern Alaska toward the end of the 3 to 7 day period. This disturbance may
bring heavy rainfall (1 inch or greater of rainfall in a 24-hour period) on
The remnants of Hurricane Beryl continue to linger in the Atlantic, but it
is not a threat to the lower-48 states. There is a disturbance currently over
the Eastern North Pacific Ocean. The National Hurricane Center is indicating a
10 percent chance of cyclone formation in 48 hours, as of 11am PDT. No related
hazards are anticipated for the U.S. at this time. For Saturday July 21 - Friday
The Week-2 period is forecast to be dominated by amplified
mid-level ridging across the western two-thirds of the CONUS and troughing
across the eastern third. This pattern favors heat across many parts of the
western two-thirds of the lower 48 states. A slight risk of excessive heat is
forecast to continue for western areas throughout the majority of Week-2, with
some extension further southward possible into the Central Valley of
California. Daily high temperature anomalies of +8 degrees F or more continue
to be indicated by the GEFS ensemble mean, while GEFS reforecast support a
better than 20% chance of highs above the 85th climatological percentile.
Troughing across the eastern third of the CONUS favors enhanced chances for
above-normal precipitation during Week-2 across this region. The greatest
likelihood for above-normal precipitation is over the coastal part of the
Mid-Atlantic. Mid-level ridging is anticipated to build across Alaska, favoring
a shift to above-normal temperatures, compared to the cooler temperatures
expected for Week-1.
This mid-level ridge may also support excessive heat across parts of the
Desert Southwest. A slight chance is highlighted across the region for Jul 21
to 24, with a moderate chance identified for a smaller embedded region across
the southern parts of the Desert Southwest. Parts of this area has a 20 percent
chance or greater of heat values exceeding 110 Deg F and reaching the 95th
percentile or greater. Maximum temperature anomalies may be 8 Deg F or greater
compared to normal.
A slight risk of excessive heat is highlighted over the Southern Plains
throughout Week-2, with a moderate risk across interior Texas, July 21 to 23.
The cold front in the Great Plains during Week-1 is not forecast to make it
this far south, resulting in lingering heat and moisture across the region.
Heat risk guidance from the GEFS and ECMWF highlights parts of the identified
area reaching the 95th percentile, with heat index values reaching 110 Deg F or
greater. Both the GEFS and ECMWF heat tool is showing a stronger signal with
greater spatial area for excessive heat across this area, compared to yesterday.
Model uncertainty continues from yesterday regarding the potential of heavy
rain associated with the North American Monsoon across the Four Corners region
in Week-2. Daily ensemble mean precipitation totals are generally on the order
of a quarter inch or less, suggesting a more widespread, showery precipitation
for the region. The Week-2 precipitation forecast indicates the most favored
area for above-normal precipitation over Colorado and western parts of the
Central Plains. While not highlighted on the forecast map, the flash flooding
risk should continue in the first half of Week-2 across this region before
things potentially quiet down.
The U.S. Drought Monitor, valid on July 10, shows a minor decrease in
severe drought coverage to 16.46 percent (from 16.64 percent). Conditions over
northern Missouri have deteriorated, although there is some improvement in
south-central Texas along the Rio Grande.
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.