Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 241123

Area Forecast Discussion
National Weather Service Bismarck ND
623 AM CDT SUN JUL 24 2016

Issued at 623 AM CDT Sun Jul 24 2016

We increased wind speeds a bit today from north central ND through
the James River valley, as model-forecast soundings show a well-
mixed layer extending to about 750 MB with mean winds from 20 to
25 kt at Minot and Jamestown. Using the consensus of recent MOS
guidance pushed forecast wind speeds into the 20 mph range with
gusts to 25 mph over a wide area than earlier advertised. The rest
of the going forecast is on track. Radar trends through 1115 UTC
show light showers in northwest SD staying to the south of the ND
state line, supporting the going dry forecast.


.SHORT TERM...(Today through Monday afternoon)
Issued at 352 AM CDT Sun Jul 24 2016

Latest water vapor imagery indicates weak cyclonic flow across
western and central ND, with a few shortwaves noted upstream. One
shortwave was located near Meadow lake, Saskatchewan; the second
was near Medicine Hat, Alberta; and the third was just east of
Livingston, Montana.

For today, the shortwave near Meadow Lake will continue to move
southeast with the GFS model just grazing Rolla with 0.01 of
precipitation late this afternoon. The NAM/RAP13/ECMWF keep it dry
and this follows the populated gridded solution, and concur. The
second shortwave mentioned above is forecast to weaken/dampen out
as mid/upper level height rises commence and suppress any threat
of showers. The third shortwave per Bowman and regional radar is
generating weak reflectivity`s into southeast Montana and
northwest South Dakota. Some lightning strikes near and southeast
of Billings, Montana. Indications are the area of showers will
come close to southwest ND by 12z Sunday, but generally remain in
western and southern ND during the morning. Thus, overall a dry
day with a few mid/high clouds with an amplifying mid/upper level
ridge taking shape today into Monday. The upper flow transitions
to northwest as a departing upper low/trough in central Ontario
continues to shift east. Pleasant temperatures under this pattern
with highs today ranging from the upper 70s north to the mid 80s

Clear conditions Sunday night under the mid/upper level ridge.
This will continue into most of Monday, however, as low level
winds turn southeasterly to southerly tonight, especially in
southwest ND, increasing moisture advection will begin. The mid
level ridging pattern shifts east resulting in a west to southwest
mid level flow and several shortwaves lining up. An initial
shortwave impinges into southwest ND late Monday afternoon. Both
the NAM/GFS pinpoint an instability axis across southwest and
into south central ND late in the day. 0-6km shear marginal at
best, ranging between 20kt and 25kt, along with 1000 j/kg of
cape. A chance of showers and thunderstorms can be expected in the
southwest, with dry conditions elsewhere through Monday afternoon.
Highs Monday will be warmer, ranging between 85 and 95.

.LONG TERM...(Monday night through Saturday)
Issued at 352 AM CDT Sun Jul 24 2016

An active weather pattern is expected this week with multiple
opportunities for showers and thunderstorms.

The 00 UTC suite of global model guidance was in relatively good
agreement advertising a gradual transition from west to northwest
500-MB flow over the northern Plains by midweek. That transition
is forecast to occur as the strong upper-level subtropical ridge
that`s been in place over the central United States retrogrades
into the Great Basin and weak mean troughing becomes established
over the Great Lakes region. As mentioned, the GFS and ECMWF and
their ensembles are consistent with this theme, as they are with
the idea that this regime will feed the region a steady diet of
weak mid-level shortwave trough passages throughout the week. A
seasonably-rich boundary layer air mass is forecast by that set
of guidance with persistent easterly low-level flow maintaining a
reservoir of dewpoints averaging in the mid 60s F most periods.
This scenario will likely drive several clusters of convection,
though predictability of individual, low-amplitude shortwaves in
the flow is low and thus the forecast is largely a broad-brushed
period of chance PoPs driven by the normally-well-verifying multi-
model consensus.

Interestingly, PoPS from the 00 UTC station/point-based GFS MOS
(MEX) guidance from Tuesday through Friday are generally in the 40
to 70 percent range for each 24-hour period. That`s well above the
seasonal climatology values near 30 percent, which is very often a
statistically-robust signal for precipitation. Even the 00 UTC GFS
ensemble members are supportive of wetting rainfall, with a mean
QPF at Bismarck this week of 0.57 inches. Of course, inspection of
that ensemble guidance reveals the typically-wide QPF distribution
one would expect with scattered convection, with total QPF ranging
from just 0.11 inches to 1.85 inches. Admittedly, more members are
lower than the mean than above it, which likely supports generally
modest confidence in the specific details of this pattern.

There will be opportunities for strong to severe storms this week
owing to steep mid-level lapse rates atop a moist boundary layer.
However, one potentially-limiting factor arguing against anything
more than a marginal risk of severe weather is relatively low-end
deep-layer shear, which is forecast to average only 30 kt in the
0-6-km AGL layer most day. However, the 00 UTC GFS indeed reveals
pockets of greater shear near 40 kt, more supportive of organized
updrafts. That implies some uncertainty and suggests that there
could be increased severe probabilities on the mesoscale and/or at
shorter lead times. Our confidence in the severe risk was too low
for any specific mention in the hazardous weather outlook yet.

Temperature-wise, the 00 UTC multi-model consensus supports highs
cooling somewhat from 85 to 90 F Tuesday to the upper 70s/lower
80s F Wednesday through Friday. A warmer and drier pattern could
emerge for next weekend as 500-MB heights rise again in response
to a shortwave trough modeled to cut across southwestern Canada
during that time.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 623 AM CDT Sun Jul 24 2016

VFR cigs/vsbys through the TAF Period with a few/sct mid and high
level clouds. West to northwest winds generally 12G20kt most
terminals this afternoon, with KMOT the strongest with G25kt.


.BIS Watches/Warnings/Advisories...


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