Valid Saturday June 03, 2023 to Friday June 09, 2023
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT May 26 2023Synopsis
: The synoptic pattern during the week-2
period is characterized by widespread mid-level high pressure over Canada and
weak mid-level low pressure along both coasts of North America. This results in
warmer and relatively quiet weather for most of the Contiguous U.S. (CONUS).
Enhanced chances for excessive heat in parts of the Midwest are anticipated to
wane early week-2, but as the anomalous mid-level ridge in Canada drifts west,
there will be slightly enhanced chances for a period of nominally-excessive
heat in the Northwest CONUS. A favorable environment for thunderstorms with
heavy rainfall in the Plains and some adjacent portions of the Lower
Mississippi Valley and Rockies should slowly relent by the middle of week-2,
when moist low-level inflow eases. The potential for river flooding mostly
related to the spring thaw continues for portions of the West CONUS, Alaska,
and along portions of the James River in South Dakota and Souris River in North
- Slight risk for heavy precipitation for
portions of the Plains and adjacent Rockies, Sat-Tue, Jun 3-6.
- Slight risk for excessive heat for portions of the Upper Midwest, and the
Ohio, Middle and Upper Mississippi Valleys, Sat, Jun 3.
- Slight risk for excessive heat for parts of the Northwest Sat-Fri, Jun 3-9.
- Possible flooding for portions of California, Nevada, Utah, Wyoming,
southwestern Montana, and Idaho.
- Possible flooding along portions of the James River in South Dakota.
- Possible flooding along portions of the Souris River in North Dakota.
- Possible flooding in parts of western Mainland Alaska and along the Yukon,
Kuskokwim, Koyukuk, and Kobuk Rivers.
- Rapid onset drought risk across portions of the Upper Midwest, and the
Middle Mississippi and Ohio Valleys.
For Monday May 29 - Friday June 02: WPC Days 3-7 U.S.
Hazards For Saturday June 03 - Friday
The week-2 synoptic picture as depicted by ensemble model
solutions for 500-hPa height anomalies resembles an omega block, with weak
troughing along both coasts of North America, slightly below-normal mid-level
500-hPa heights along the southern tier of the CONUS, and expansive mid-level
ridging over much of Canada. This general configuration continues through the
period, although the anomalous mid-level ridge centered over Canada is expected
to slowly retrogress toward western Canada and weaken slightly as the period
progresses. As a result, warm and generally quiet weather is predicted to
prevail across most of the CONUS. One exception to this is over part of the
Plains and adjacent portions of the Rockies and Lower Mississippi Valley, where
increased low-level jet (LLJ) activity creates enhanced probabilities of heavy
precipitation with periodic thunderstorms for the region until the middle of
week-2. Rainfall will be enhanced at times by upsloping orographic winds near
the mountains. Reforecast tools from the GEFS, ECMWF, and CMCE all indicate at
least a 20% probability of exceeding the 85th climatological percentile and
0.75 to over 1.0 inch for 3-day accumulated precipitation, supporting a slight
risk of heavy precipitation across the region, Jun 3-6. This slight risk area
is again extended farther north for the second successive day based on raw
output from the CMCE, ECMWF, and GEFS ensemble means.
Expansive mid-level ridging over much of central North America is likely to
result in warmer than normal temperatures across the central and northern
portions of the CONUS, closest to the maximum 500-hPa height anomalies
associated with the broad mid-level ridge centered in Canada. All reforecast
tools indicate at least a 20% chance of maximum temperature exceeding the 85th
percentile during Jun 3 from the northwestern Ohio Valley through the Middle
and Upper Mississippi Valleys and the southwestern Great Lakes Region. The
ECMWF reforecast tool and to a lesser extent the CMCE counterpart favor a
warmer solution with 30% to 50% probabilities of exceeding the 85th percentile,
but GEFS-based tools are cooler and bring in significant uncertainty,
precluding designating any areas with a moderate risk of excessive heat. Dew
points and associated heat indices are not expected to be extremely elevated,
but nonetheless there is the potential for temperatures to exceed 90 deg F for
portions of the Upper Midwest for the first time this season. The past one to
two months have been drier than normal in this region, which increases the odds
for higher temperatures but limits the potential for unusually high dew points.
Taking all of this into consideration, a slight risk of excessive heat is
posted from western Indiana westward through northern Missouri and northward
across southern Minnesota, including part of the Chicago metro area, Jun 3.
Ensembles overwhelmingly favor a slow retrogression and de-amplification of
the expansive ridge over Canada, which should bring much above-normal
temperatures to the northwestern CONUS throughout the period. There is still a
lot of uncertainty regarding the potential for hazardous heat, but with
positive 500-hPa height anomalies over and north of the region throughout
week-2, chances are sufficiently elevated to post a slight risk for excessive
heat over the Northwest throughout the period (Jun 3-9), with the best chances
near the middle of week-2. Probabilistic tools show lesser chances for
impactful heat to the west of the Cascades, and the lower-level wind flow
pattern is not particularly favorable to bring excessive heat west of the
Cascades, so the hazard has been removed from this area. In contrast,
probabilistic tools based on all three model ensembles show enhanced chances
for temperatures topping 90 deg. F in parts of central and southwestern Idaho,
so the slight risk hazard has been extended into this region.
Drought concerns are forecast to increase across parts of the central and
eastern Corn Belt and adjacent areas during week-2 due to the aforementioned
warmth, the expectation of below-normal precipitation, and precipitation totals
one to three inches below normal for the past 30 to 60 days. Soil moisture is
currently below the 30th climatological percentile over many of these areas.
Due to these factors, a rapid onset drought risk is highlighted across parts of
the central and eastern Corn Belt, specifically in much of southern Iowa,
northern Missouri, central Illinois and Indiana, and southern Ohio.
Snowmelt continues across the western CONUS after accumulating a very large
and in some cases record-breaking snowpack, inducing river flooding especially
across higher elevations for some areas in the West, where a few sites still
report over 40 inches of snow water content. As snowmelt continues in parts of
the Sierra Nevada, Great Basin, and Northern Rockies, flooding may continue to
occur along some rivers and in areas adjacent to the higher elevations.
Flooding is also expected to continue along the James River in South Dakota as
river levels have been very slow to recede due to saturated ground conditions
and relatively flat topography. A similar situation has developed along the
Souris River in North Dakota, which should cause ongoing minor to moderate
flooding to continue into week-2.
Weak mid-level flow across Alaska favors only a slight tilt in
probabilities for above and below normal temperatures across parts of northern
and southern Alaska, respectively. However, regardless of temperatures, rivers
are expected to continue to rise across western Mainland Alaska due to ice
jams, while increasing snowmelt across eastern Alaska is anticipated to
continue the potential for river flooding through a large part of the Alaskan
Interior. Other rivers of concern for river ice break up leading to the
potential for possible flooding and ice jams are the Kuskokwim, Koyukuk, and
Kobuk Rivers. Another factor which could impact conditions over parts of Alaska
is the evolution of Super Typhoon Mawar, currently west of Guam in the Pacific
Ocean with top winds near 175 mph. Mawar is now the strongest typhoon since
2021, and the fifth-strongest May typhoon on record. The typhoon is expected to
continue westward for the next few days before turning to the northeast just
east of Taiwan. After recurvature, the storm is anticipated to slowly become
extratropical while continuing northeastward, but still remain a potent storm
system. Some tools bring the remnants of Mawar close to Alaska during week-2,
which would significantly impact some parts of the state. However, model
guidance has been inconsistent regarding how far north the storm tracks, and
today’s runs are less indicative of a potential threat to Alaska than
yesterday, so there are no highlighted hazard risks associated with the
remnants of the typhoon at this time.
Forecaster: Rich Tinker
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts