Valid Friday July 03, 2015 to Tuesday July 14, 2015
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT June 30 2015Synopsis
: A frontal boundary is expected to be
the focal point for unsettled weather across the central and eastern U.S.
during the first several days of the period. Upper-level high pressure is
forecast to dominate over the northwestern U.S. early in the period, expanding
northwestward toward mainland Alaska later in the period. Periodic unsettled
weather is expected over parts of the Southwest extending into the central
Rockies, increasing in frequency heading toward the middle of the period.
Detailed Summary For Friday
July 03 - Tuesday July 07:
- Much above-normal temperatures for parts of the
Northwest, including far northern parts of California and Nevada, Fri-Tue, Jul
- Heavy rain for parts of Arkansas and the Tennessee River Valley, Fri-Sat,
- Enhanced wildfire risk for parts of mainland Alaska, Fri-Tue, Jul 3-14.
- Slight risk for much above-normal temperatures for the Pacific Northwest
and parts of the northern Rockies, Wed-Tue, Jul 8-14.
- 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 amplified
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, including northern California for
this entire period. Some of these areas may experience temperature anomalies of
24 degrees F or greater above climatology, with temperatures reaching the
triple digits. Because of the long duration of these anomalously warm
temperatures, people outdoors or without air conditioning should take
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 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 frontal boundary is expected to focus
locally heavy rainfall extending from parts of eastern Oklahoma eastward
through the Tennessee Vally into the Mid-Atlantic. The threat for heavy rain is
greatest on Thursday and Friday where the hazard is depicted, with increased
uncertainty beyond that, as the frontal zone is forecast to slowly move north.
This increases odds for locally heavy rain over parts of the Midwest and Great
Lakes by the end of the period.
To the southeast of the front, hot and humid conditions are likely,
especially during the middle and latter parts of the period when the
upper-level trough weakens and the frontal zone retreats northward. The
excessive heat hazard is depicted as such due to the greatest likelihood of
maximum heat index values exceeding 105F for multiple days.
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. An upper-low is forecast to impact the Alaskan
panhandle at the beginning of the period, and some active weather is possible
over the Aleutians late in the period, though neither currently warrants any
additional hazards being specified. For Wednesday July 08 - Tuesday
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. Within that
region the threat of much above-normal temperatures is moderate for the first
three days of the period over the interior Pacific Northwest. However, the
forecast pattern looks potentially less amplified than that for 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.