Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 231143

Area Forecast Discussion
National Weather Service Bismarck ND
643 AM CDT Mon May 23 2022

Issued at 643 AM CDT Mon May 23 2022

The going theme of the forecast is on track, so all we did with
this update was blend observed trends into it for the morning. As
of 1130 UTC, scattered showers are most focused along a line from
Killdeer to Bismarck and Ellendale, and will continue moving north
through the morning in tandem with midlevel warm air advection.


.SHORT TERM...(Today and tonight)
Issued at 346 AM CDT Mon May 23 2022

The key message in the short term period is for scattered showers
and thunderstorms today into this evening.

Early this morning, midlevel warm air advection maximized near the
terminus of a modest low-level wind maxima centered around 850 mb
is generating a few showers that are shifting northward with time
into southwest and south central ND. This is occurring downstream
of a weak shortwave trough that has its axis roughly alone a line
from Havre, MT, to Salt Lake City, UT as of 08 UTC. Water vapor
imagery reveals both the strongest post-trough drying and implied
downstream forcing manifest as a modest baroclinic leaf signature
with the southern portion of this shortwave trough. Extrapolating
those satellite signatures suggests guidance expectations for the
greatest synoptic-scale forcing with this trough to remain south
of the local area are well on track.

Regardless, the northern portion of the middle- and upper-level
trough will continue slowly shifting eastward today, into western
ND this afternoon. The aforementioned warm air advection centered
around 850 mb is forecast to continue downstream of the trough
today, while its maxima gradually shifts northward, which supports
both continuation of early-day showers and gradual propagation of
them northward through central ND through the day. CAMs support
early-day radar trends in this activity being somewhat scattered.

By this afternoon, steep midlevel lapse rates associated with cold
temperatures aloft and a gradually warming boundary layer (with
highs today forecast in the 60s F) will contribute to MLCAPE from
300 to 700 J/kg. Residual CIN will be minimized once temperatures
reach about 65 F, supporting development of scattered deep moist
convection by 21 UTC amid broad height falls aloft. The lack of
well-defined surface convergence suggests exact locations favored
for thunderstorm development are less-certain than usual, and we
accordingly took a more broad-brush approach to PoPs through the
day today compared to individual CAMs and the NBM. Some CAMS such
as the HRRR from its 00 through 06 UTC cycles, focus simulated
convection along a weak wind shift at 850 mb that develops as the
trough axis aloft approaches. However, a wide variety of outcomes
are simulated in other CAMs, and given weak overall forcing, we
again took a more broad-brushed approach to our forecast and are
messaging scattered showers and thunderstorms area-wide. Given
weak bouyancy and weak deep-layer shear of 20 to 25 kt, we expect
weak and multicellular convection to occur. Cold thermal profiles
and steep lapse rates do suggest small hail will occur with the
strongest updrafts at times, though. The 00 UTC HREF local
probability-matched mean QPF suggests isolated half-inch rainfall
totals are possible with the strongest storms, too, but the NBM-
based probability of a half inch of rain at any given location is
only 5 percent. The probability of any specific location receiving
a quarter inch of rain today is also only near 25 percent, again
reflecting the scattered nature of convection, and the modest
tropospheric moisture content available today.

We expect a gradual downward trend in convection this evening as
the boundary layer cools and bouyancy diminishes. Lows tonight
will once again be seasonably cool, from 35 F in the southwest to
the lower 40s in north central ND and the James River valley.

.LONG TERM...(Tuesday through Sunday)
Issued at 346 AM CDT Mon May 23 2022

The theme in the long term forecast period remains a warming trend
through late week, with an increasing chance of precipitation by
next weekend.

Synoptically, a mean upper-level trough will be centered over the
central U.S. through the middle part of the week. Trends in global
ensemble guidance have been for this trough to persist longer with
lower heights, which in turn may allow for weak impulses to cross
the Northern Plains Tuesday and Wednesday. Enough consensus exists
in one such impulse for the NBM to generate a slight chance of
showers Wednesday, which we are carrying in the official forecast.
Despite some uncertainty in the synoptic evolution in this time
frame, spread in global ensemble temperature guidance remains very
low Tuesday through Thursday, with the 25th to 75th percentiles
of NBM membership 5 degrees F or less. Confidence is thus high in
forecast highs warming from the 60s F on Tuesday and Wednesday to
the 70s F Thursday.

Late this week and into next weekend, a new upper-level trough is
forecast to move into the Pacific Northwest and eventually reach
the Northern Plains. Guidance remains in several camps with this
trough, varying from a faster, lower-amplitude passage with less
temperature change and less precipitation, to a slower, deeper
trough. The latter scenario would cause both warmer temperatures
Friday and Saturday ahead of the trough, and ultimately would be
favorable for higher precipitation chances. At this point, both
scenarios are plausible outcomes, so the forecast follows the
multi-model consensus with gradually cooling temperatures after
highs approaching 80 F on Friday, along with an increasing chance
of showers and thunderstorms next weekend.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 643 AM CDT Mon May 23 2022

VFR conditions will generally prevail today and tonight, but
scattered showers this morning will gradually expand in coverage,
with scattered thunderstorms also developing after about 21 UTC.
Local sub-VFR conditions are possible with thunderstorms this
afternoon and evening. Uncertainty in exact timing and location of
thunderstorms prevented more than a VCTS mention in any of the 12
UTC TAFs, though. Showers and storms will diminish after about 03
UTC tonight.




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