Area Forecast Discussion
Issued by NWS Dodge City, KS

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FXUS63 KDDC 290528
AFDDDC

Area Forecast Discussion
National Weather Service Dodge City KS
1228 AM CDT Sat Apr 29 2017

...Updated Aviation Discussion...

.SHORT TERM...(This evening through Saturday)
Issued at 258 PM CDT Fri Apr 28 2017

...HIGH IMPACT STORM THIS WEEKEND WITH HEAVY WET SNOW...

Major spring storm with winter impacts this weekend -- complete with
all sorts of forecast challenges -- and what it will all really come
down to is surface temperatures.

Early this afternoon, observations were showing snow across much of
western and central Nebraska, and the GFS and NAM12 wet-bulb zero
heights at or below 1000 feet AGL seemed to be a good delineation
between rain vs. snow up there. This will be a good tool for
forecast rain vs. snow in our part of the world tomorrow and
Saturday.

A major mid-latitude cyclogenesis event will be taking place just to
the south of southwest Kansas as surface cold air will be filtering
in from the north. The first wave of warm advection/frontogenesis
precipitation will occur this evening, and POPs will be ramping up
significantly after 00z this evening. The first question will be how
soon rain will change to snow in the Hamilton County area late
tonight. The GFS and NAM both show sub-1000 ft AGL WBZ heights,
supporting snow at the surface, reaching Syracuse to Scott City area
by 09z early Saturday morning. The ~1000ft AGL WBZ line will then
likely reorient itself a bit to a more north-south orientation later
in the morning, extending from roughly Hugoton to Garden City to
Dighton by 15z.  East of this line...rain.  West of this
line...snow. Late April indirect insolation will no doubt play at
least a small role in limiting the eastward push of the rain-snow
line, and it will probably remain quasi-stationary through the day
somewhere around or just east of the U83 to K23 corridor.

The GFS and NAM are showing substantial QPF even in the
aforementioned snow areas all day Saturday -- anywhere from 0.50 to
0.80 inch. By early evening Saturday, this would likely equate to 3
to 6 inches of snow using a conservative 6-8:1 snow-to-liquid ratio.
The snow will be very wet, most likely all falling at temperatures
of 33 or 34 degrees. There should be quite a bit of melting from
beneath given heat flux from the warm soil temperatures (2 to 8 inch
soil temperature at DDC was in the lower 50s). We are quite
concerned, though, that despite any melt rate, 1 inch-per-hour
snowfall rates would be more than sufficient to combat at slower
melt rate. The significant amount of foliage on trees this late into
April is of greatest concern -- as 6 inches of snow will definitely
cause problems given the high water content of snow accumulating on
exposed foliage.

This takes us into Saturday Night when the main upper low starts to
undergo rather impressive deepening across the Texas Panhandle. The
700mb low will likely undergo major cyclogenesis as well, which will
greatly enhance frontogenesis at that level just to the north of the
700mb low center itself. The ECMWF has been locked in for at least a
couple runs now, deepening the 700mb low from 298 decameters just
east of AMA at 06z Sunday to 286 decameters very near Medicine Lodge
18z Sunday. This type of deepening supports major accumulations of
precipitation around or in excess of one inch just in the
deformation zone itself on Sunday! Much of this precipitation would
be in the form of wet snow west of Highway 283. For this reason, we
would likely need to expand the Winter Storm Watch eastward to the
U283 corridor (Dodge City to Wakeeney) given the major concerns in
deformation zone wet snows.

To wrap this up, when all is said and done, the coldest, strongest
models, like the ECMWF, support a large swath of 6+ inches of
(damaging) very wet snow.  Within this large swath, 10+ inches
cannot be ruled out, which would almost certainly cause some
substantial tree damage and power interruptions...especially with
the forecast winds during the height of the storm at 30 to 40 mph,
gusting to 55+ at times. Areas southeast of an Ashland to Greensburg
to Larned line should remain all rain for much of the event.  There
will probably be a fine gradient between the damaging, very heavy
wet snow and all rain.

.LONG TERM...(Saturday night through Friday)
Issued at 258 PM CDT Fri Apr 28 2017

After the storm departs, we will be left with remnant snow cover,
especially in any areas that receive 8+ inches. There will be rapid
snowmelt, even through the night given heat flux from warm sub-
surface soil given the time of year. Once we clear out, temperatures
should not have that far to go to get below 32, and perhaps even 28
degrees in the far western counties. Going into next week, we are
tracking another (much weaker!) storm system diving southeast from
the Northern Rockies, which will act on a pre-existing frontal zone,
leading to another chance for precipitation. Timing on this would be
Tuesday Night into early Wednesday. Another cold rain event would
likely occur with this one. After that, toward end of next week, a
much drier pattern with upper level ridging expanding across the
Rockies and adjacent High Plains. Remnant surface high will remain
across much of Kansas, even through the end of next week, preventing
any marked warmup.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1225 AM CDT Sat Apr 29 2017

MVFR and IFR ceilings can be expected over the next 24 hours as
occasional light to moderate rain continues across western Kansas.
There may be a break in this precipitation Saturday morning which
could allow for brief improvement in ceilings but still am
favoring MVFR conditions. Gusty north winds at 20 to 25 knots are
expected overnight and Saturday so although some patchy MVFR
visibilities in fog will be possible...dense fog is not
anticipated.

The rain in the GCK area is expected to mix with before changing
over to all snow between 09z and 12z Saturday. At this time it
appears that snow accumulation around the GCK airport between 12z
Saturday and 06z Sunday will be between 1 and 2 inches. Further
east mainly rain with rainfall totals over the same time frame
ranging from 0.75 to 1.5 inches.

&&

.PRELIMINARY POINT TEMPS/POPS...
DDC  34  38  33  37 / 100 100  80  80
GCK  32  35  32  34 / 100 100  80  80
EHA  32  34  30  41 / 100 100  80  60
LBL  33  38  31  39 / 100 100  80  70
HYS  34  39  35  35 /  90 100  90  90
P28  44  48  38  45 / 100  80  80  70

&&

.DDC WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from 7 AM CDT this morning through Sunday
evening for KSZ030-031-043>045-063-064-076>078-086-087.

Winter Storm Warning from 4 AM CDT /3 AM MDT/ early this morning
to 7 PM CDT /6 PM MDT/ Sunday for KSZ061-062-074-075-084-085.

&&

$$

SHORT TERM...Umscheid
LONG TERM...Umscheid
AVIATION...Burgert



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