Valid Saturday July 27, 2019 to Friday August 02, 2019
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT July 19 2019Synopsis
: 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. Early in
Week-2, a stalled front across the Southeast and Texas may bring above normal
precipitation to the western Gulf Coast. Models indicate the potential for a
series of surface low pressure systems across the Bering Sea during Week-2,
supporting anomalously high wind speeds across parts of western and southern
Alaska during the first couple of days of Week-2. 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.
- Moderate risk of excessive heat for portions of
California, Sat-Wed, Jul 27-Jul 31.
- Slight risk of excessive heat for portions of the western third of the
CONUS, Sat-Thu, Jul 27-Aug 1.
- Flash flooding possible across portions of the Four Corners region.
- Slight risk of much above normal temperatures for portions of the Alaska
Panhandle, mainland Alaska, and the Aleutians, Sat-Thu, Jul 27-Aug 1.
- Slight risk of high winds for portions of mainland Alaska, Sat-Sun, Jul
For Monday July 22 - Friday
July 26: WPC Days 3-7 U.S.
Hazards For Saturday July 27 - Friday
Amplified mid-level high pressure is forecast to dominate the
western half of the CONUS throughout Week-2. A slight risk of excessive heat
across the western third of the CONUS is highlighted, July 26 - August 1, and a
moderate risk of excessive heat is embedded within over central California for
the same time period. The GEFS reforecast tool forecasts a broader region of
maximum temperatures exceeding the 85th climatological percentile than the
ECMWF tool, but the ECMWF tool has higher probabilities (40-60%) of excessive
heat over central interior California. A large spatial area was chosen due to
the potential of this being a multi-day heat event.
The positioning of the mid-level ridge across the western CONUS may
continue the increased likelihood of locally heavy rain 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 flash 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 trough 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, but our calibrated model guidance does not currently suggest that
enough rain will fall to warrant a posted hazard.
There are indications that high pressure over the northeastern part of the
country could lead to anomalously warm temperatures over northeastern New
England during the first few days of August. However, we haven't posted a
related hazard since dynamical guidance keeps maximum temperatures in the low
to mid 80s.
A series of surface lows is anticipated over the Bering Sea 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 27-28. 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. A slight risk of much above normal temperatures is
posted across parts of mainland Alaska, July 27 to August 1. 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 1.66 million acres have burned statewide (as of July
18th, 2019) since the beginning of the year.
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts