Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 241157 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
657 AM CDT Mon Apr 24 2017

.UPDATE...
Issued at 644 AM CDT Mon Apr 24 2017

See below for an aviation forecast discussion for the 12Z TAFs.

&&

.SHORT TERM...(Today through Wednesday Afternoon)
Issued at 403 AM CDT Mon Apr 24 2017

Looks like spring is on hold for the next few days. Low pressure
moving over Pierre now and continuing east through the course of the
day has already dislodged some very cool air, with Mobridge having
fallen to 38 degrees and sub-freezing temperatures just across the
border into North Dakota.  While the system is weakening and light
shower activity is expected to only generate a few hundredths of QPF
- the continued progression east means that locations east of the
James valley could see highs still into the 60s while to the west it
will be a struggle to reach 50.

High pressure nosing out of Canada/North Dakota will provide a
continuous feed of weak cold advection through the course of the
short term. The high never settles overhead with a storm track just
to the east, so we will never experience ideal radiational
conditions, however 850mb temperatures will be 1 to as low as 2
standard deviations below climo.

We will see a second, slow moving wave move across the plains late
Tuesday and through most of Wednesday. There remains some
discrepancy over the track of this system between deterministic
members, with - as per usual - the 00Z NAM is the most aggressive
in predicting snowfall. Thermal profiles in the GFS do support
snow however, though the other major models have a less favorable
intensity/track of a system to bring widespread accumulating snow
to CWA. The most likely area would be Sisseton hills thanks to
elevation (with a freezing level around 1400ft - the extra
elevation will help) and the timing (early Wednesday). Ground
temperatures are fairly warm, at around 50F, so it will take some
intensity of snowfall to accumulate over melting, and this far out
don`t have the confidence over whether this will occur - and thus
snow may be nothing more than a novelty in the forecast at this
point.

Late addition: the 06Z NAM is much more in line with the 00Z GFS -
with only some small accumulations for the Sisseton hills.
Elsewhere precipitation timing coincides with daytime heating
which at this time of year, will likely preclude snow reaching the
surface before melting - and if it does - melting on contact.

.LONG TERM...(Wednesday Evening through Sunday)
Issued at 403 AM CDT Mon Apr 24 2017

A pronounced split flow pattern exists off the west coast of NOAM.
Models predict this pronounced split flow pattern will be moving a
bit further south and east early this week along the Pac NW coast,
where it will remain until this weekend. At that point, the upper
flow pattern appears to consolidate into something a bit more
manageable/predictable, which includes a persistent large upper
level longwave trof over the western/southwestern U.S. and the
potential for a couple of synoptic-scale large upper low pressure
systems to impact the central part of the country.  The low
predictability that split flow brings has been evident the past few
mornings, as models have shown rather poor run-to-run consistency
and compared to each other. The bottom line for this cwa is,
depending on the track these larger systems take, there could be a
couple of noteworthy precip-makers lifting north-northeast across
portions of the northern plains between Wednesday night and next
Monday. Given the low predictability and forecast confidence in the
current extended forecast, did not mess around with Superblend
guidance pops. It does appear as though Superblend has caught up to,
or at least is now trending toward, the colder than climo normal
temperatures being forecast in the out periods. The 00Z NAEFS output
continues to support the 00Z deterministic models for temperature
including one or more standard deviations below climo normal output
at 850hpa from Wednesday night through early next week. Given the
below normal cold that will be in play, precipitation chances
continue to be a combination of rain, snow or rain/snow mix.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
Issued at 644 AM CDT Mon Apr 24 2017

Mainly VFR conditions are still expected through the day for all
locations except MBG where ongoing sub-VFR ceilings should last
pretty much throughout the entire TAF valid period. Sub-VFR
stratus clouds are expected to overspread KABR, KPIR and KATY
later after 00Z. Currently, it appears KATY is the only terminal
left on the warm air side (generally southerly breezes here) of a
cold frontal boundary splayed out southwest to northeast across
the region (northerly winds at KABR, KMBG and KPIR to prevail). By
late afternoon this frontal boundary should be working through
KATY, turning winds there around to the north-northwest. Regional
radar mosaic indicates the potential for an isolated to widely
scattered shower may persist for another hour or two at KPIR and
KMBG before precipitation chances transition over to KABR and
KATY for a few hours this morning and afternoon, respectively.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...Dorn
SHORT TERM...Connelly
LONG TERM...Dorn
AVIATION...Dorn



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