Valid Saturday July 04, 2015 to Wednesday July 15, 2015
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT July 01 2015Synopsis
: A series of cold fronts are forecast
to impact the central and eastern part of the Lower 48, while upper-level high
pressure is expected to impact regions from the Southwest U.S. to mainland
Alaska. Low pressure is expected to bring active weather to the Aleutians and
far western Alaska during the period. Hazards
Detailed Summary For
Saturday July 04 - Wednesday July 08:
above-normal temperatures for parts of the Northwest, Sat-Wed, Jul 4-8.
- Heavy rain for parts of eastern Oklahoma, Arkansas, and the Tennessee River
Valley, Sat, Jul 4.
- Heavy rain extending from parts of the Southwest northeastward to Kansas,
Mon-Tue, Jul 6-7.
- Enhanced wildfire risk for parts of mainland Alaska, Fri-Tue, Jul 3-14.
- Ongoing, likely, or possible flooding across parts of the Midwest,
mid-Mississippi Valley, and the Southern Plains.
- Severe drought for parts of the western third of the CONUS, and southern
At the beginning of this period, an
upper-level ridge is forecast over the western third of the CONUS with a trough
downstream centered near the Great Lakes. This pattern favors much above-normal
temperatures across parts of the Northwest for this entire period. Some of
these areas may experience temperature anomalies approaching 20 degrees F or
greater above climatology, especially early in the period. Because of the long
duration of these anomalously warm temperatures, people outdoors or without air
conditioning should take precautions.
Over the southwestern CONUS, a combination of remnant cold fronts and
increased monsoonal flow out of the south is likely to lead to periods of
locally heavy rain, spreading northward later in the period. While there is
still not sufficient confidence to warrant a specific hazard depiction, updated
local forecasts should be monitored for the increasing potential of localized
heavy rain and flooding over the next one to two weeks.
Over the central and eastern CONUS, a stalled frontal boundary at the
beginning of the period is expected to focus locally heavy rainfall over parts
of the Tennessee Valley. The threat for heavy rain is greatest on Friday and
Saturday where the hazard is depicted, with increased uncertainty beyond that,
as the frontal zone is forecast to slowly move north as a warm front ahead of
the next shortwave trough and associated surface low. Within the depicted
hazard, some areas could receive over 2 inches of rain during the period.
To the southeast of the front, hot and humid conditions are likely, though
the latest guidance suggests that heat index values will not warrant a depicted
hazard at this time.
As a forecast upper-level trough swings through southern Canada during the
period, surface low pressure and an associated cold front are expected to
impact the northern Plains, upper Midwest, and Great Lakes, resulting in
cooler-than-normal temperatures and increased rain chances by late in the
period. Currently there is insufficient model support for a heavy rain hazard.
Warm and dry conditions are anticipated across much of mainland Alaska,
increasing chances for wildfire risk across parts of this area during this
period as well as Week-2. Active weather is possible over the Aleutians during
the period, though no additional hazard depiction is warranted. For Thursday
July 09 - Wednesday July 15:
During Week-2 the forecast circulation is
dominated by positive 500-hPa height anomalies centered over the Gulf of Alaska
with downstream troughing centered over the Great Lakes. The ensemble means
indicate that the ridging over the northeastern Pacific and Alaska is part of a
rex block at least early in the period, with an anomalous trough forecast to
the south, just off the coast of California. Such a pattern favors increased
rainfall associated with multiple cold fronts extending from the central Plains
to the Northeast. A combination of stalled cold fronts and anomalous southerly
flow will lead to increased chances of locally heavy rain and flooding for
parts of the Southwest and Great Basin.
Anomalous ridging over Alaska increases the chances of dangerous fire
weather, and so the hazard depicted in the 3-7 day period continues into Week-2.
With persistent ridging forecast just off the Northwest Coast, a slight
risk of much above-normal temperatures continues through Week-2. However, the
forecast pattern looks potentially less amplified than that for the early part
of the 3-7 day period, as the height pattern exhibits some retrogression and
undercutting is possible late in Week-2.
The most recent U.S. Drought Monitor, valid on June 23, indicates a small
increase (from 13.62 to 14.31) in the percentage of the CONUS in severe to
exceptional drought (D2-D4).
Forecaster: Stephen Baxter
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.