Area Forecast Discussion
Issued by NWS Grand Forks, ND

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884
FXUS63 KFGF 222010
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
310 PM CDT Sat Apr 22 2017

.SHORT TERM...(This evening through Sunday)
Issued at 310 PM CDT Sat Apr 22 2017

Very challenging forecast, mainly due to the snowfall expected
tonight. As of mid afternoon, the cold front had sagged to a
Bemidji to Valley City line. Cooler temperatures, north winds, and
a mix of clouds and sun were occurring behind the front, while
temps have risen to the mid 60s ahead of the front. The thickest
clouds were right along the Canadian border, where the radar also
showed some echoes. Web cams show wet snow falling around Cavalier
ND. These echoes will continue to progress eastward through the
late afternoon and early evening. Bigger story will be later
tonight into at least mid to late Sunday morning, and that
involves the snow. Models have shown the potential for a band of
convective type snow developing somewhere in the 3 am time frame
and continuing through mid to late Sunday morning.

Being convective snow, it would not take a lot to get a couple
inches of snow. There is strong lift, decent moisture, and
instability. At this point it appears that this would be most
favorable along and just south of the highway 2 corridor, but this
could shift a little too. Within this, there is a potential of a
narrow band of heavier snow, of up to 6 inches or so, over a very
thin band. Like summer storms, there is little idea where it will
develop until it actually occurs. For now, have issued a special
weather statement to highlight the area affected. If later shifts
can observe where the narrow snow band sets up, they can add more
certainty to the forecast. The snow should be mainly confined to
the Grand Forks to Bemidji corridor by late Sunday morning, with
slowly improving conditions through the afternoon. Had good
coordination today with WPC and Bismarck and Duluth.

.LONG TERM...(Sunday night through Saturday)
Issued at 310 PM CDT Sat Apr 22 2017

Sunday night and Monday...The models are all in fairly decent
agreement on a fast moving but potent shortwave trough moving
through the Plains and into MN. Will continue to keep fairly high
POPs going with precipitation totals ranging from a few tenths to
over three quarters of an inch. Where they differ is in the exact
track of the surface low and how fast and far north the warm front
goes Sunday night and the cold front comes down on the backside of
the system on Monday. There should be a pretty tight temperature
gradient across the CWA Sunday night and Monday with morning
temperatures near the freezing point in the north but the low 40s in
the south. NAM models soundings develop a pretty good warm layer
aloft late Sunday night into Monday morning across the northwestern
counties, with the possibility of a wintery mix of IP or FZRA. The
GFS on the other hand, is not nearly as robust with the warm layer
and has more of a rain/snow mix. Ensemble probabilities have some
low chances for wintery mix precip, but are hitting snow and rain
harder. Will continue to keep a mention of IP/FZRA going for a brief
period near the highway 2 corridor, but at this point think that it
will be fairly fleeting. Precip should be more snow near the
Canadian border. For now have accumulations pretty light but will
watch for banding features in the future as some of the models have
some good 850mb frontogenesis Sunday morning although it runs ahead
of the best synoptic forcing.

Tuesday through Thursday...There will be a brief break between
systems but another shortwave trough will lift from the Central
Plains into the Great Lakes during the mid-week period. At this
point most model runs take the system well to our south although the
ECMWF has a much further northwest solution with precip impacting
our southeastern counties. Since that seems to be an outlier will
continue to keep only minimal POPs in our southeast. Temps will be
cool for late April with highs only in the 40s Tuesday and Wednesday
with only a bit warmer readings for Thursday.

Friday and Saturday...Another weak system moves by to our south on
Friday, although the models seem to indicate another upper trough
moving into the Plains on Saturday. Depending on the exact track our
south and east could see precip, but uncertainty is high at this
point. Temperatures will continue to be a bit cooler than average
for the end of the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1245 PM CDT Sat Apr 22 2017

Low clouds have made it into KDVL/KGFK/KTVF, but will take a while
yet to reach KBJI and KFAR. Timing the front shows it into KBJI by
3 pm and KFAR by 5 pm, give or take a little. IFR to MVFR clouds
remain behind the front, and don`t anticipate these clouds to rise
too much during the day hours today. Bigger challenge tonight will
be snow chances. Like mentioned earlier, there is a potential for
a band of snow to fall somewhere along the highway 2 corridor,
mainly in the 3 am to 10 am Sunday time frame. There could be some
areas along this line with very intense snow rates, with
visibilities near zero and very low ceilings. For now have kept
vsbys in the 1 mile range, but they could be much worse. This will
be a convective snow, with the heaviest snow being in a fairly thin
band. This can only be determined once the event starts, so there
will not be much lead time on it. So for now the 1 mile
visibility is heads up, with the timing the best available at the
moment.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
&&

$$

SHORT TERM...Godon
LONG TERM...JR
AVIATION...Godon



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