Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

750
FXUS63 KEAX 062327
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
527 PM CST SAT FEB 6 2016

.DISCUSSION...
Issued at 305 PM CST SAT FEB 6 2016

The main forecast concern for this forecast deals with potential
convectively induced snow showers late Sunday night through the day
Monday.

Models show a very strong upper level PV anomaly sliding southeast
through the Northern/ Central Plains and diving into the Southeast
Sunday night into Monday. This will have several distinct impacts on
the weather in the area. First, with the surface front moving through
late Sunday morning or early in the afternoon, deeper mixing will
develop with parcels mixing into winds around 35 kts in the 0.5KM to
1.5KM AGL layer. The winds in this layer increase overnight, as the
PV anomaly is moving through, and lapse rates remain steep into this
layer. So winds will likely be very strong and gusty overnight.
Shortly after sunrise, lapse rates continue to steepen into these
strong winds aloft so there will likely be a period of time Monday
morning where winds are gusting 40 to 45 mph with sustained winds
around 30 mph. This alone would likely need a wind advisory but there
will be another aspect with this passing system which may have a
greater impact.

With the strong PV anomaly moving through, inducing steep low level
lapse rates, there will actually be at times 50+ J/kg surface based
CAPE, even in the pre-dawn hours. While moisture will be limited,
the dendritic growth layer is saturated and is relatively deep.
This indicates that 1) there will be ice crystals present and 2)
snow ratios will be well above our normal 13:1. In fact, snow ratios
will likely reach and possibly exceed 20:1. So while QPF will be
meager, probably less than 0.05" liquid, snow amounts will likely be
around half an inch to up to an inch. But let`s not focus on the
light amounts, rather the showery, convective nature to the snow.
This may result in very brief but blinding snow fall, especially
given the strong winds that will be present. For anyone that
remembers the February 14th, 2010 snow event, the amounts that day
were insignificant. Rather, it was the sudden onset of blinding snow
showers that caused multiple, many vehicle pileups on area
interstates. The setup with for this event looks very similar except
for the timing of the maximum PV moving over which that day was mid
morning/early afternoon. While the max PV for Sunday night and
Monday will occur overnight, comparing forecast soundings between
the two events shows the similarities. Thus, the important messaging
isn`t the snow amounts, but rather that one may drive into an
intense area of snow, a whiteout, and not be able to see. It`s
possible this may happen during the Monday morning commute given the
forecast soundings from across the area. Additionally, the BTV snow
squall parameter, which takes into account low level moisture,
instability, winds and temperatures, reaches very favorable values
Monday morning. This parameter supports the pattern recognition for
this event and only increases confidence.

Regarding potential headlines for this event, it`s quite possible a
winter weather advisory will be needed. Not for the snow amounts but
rather for the potential impacts. For now, since it`s beyond 24
hours away, will hold off any headlines and increase wording in the
HWO briefing packet.

For now, the rest of the forecast looks relatively quiet with no
major systems depicted by the medium range models. While
temperatures the first half of the work week look below normal,
there should be a trend to closer to or above normal for the later
half of the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 514 PM CST SAT FEB 6 2016

The main impact with this forecast will be in the form of increasing
winds overnight, persisting well into Sunday afternoon. Southwesterly
surface winds will turn northwesterly as a cold front crosses the
area early Sunday morning. Prior to this transition, winds around
2kft will rapidly accelerate to 45-50kts overnight, which coupled
with more stable winds at the surface will translate to wind speed
shear before surface winds increase behind the frontal passage Sunday
morning. Heading into Sunday afternoon, sustained surface winds of
20kts gusting to around 30kts will make for turbulent departure and
arrival conditions before wind gusts slacken Sunday evening.

&&

.EAX Watches/Warnings/Advisories...
KS...NONE.
MO...NONE.
&&

$$

DISCUSSION...CDB
AVIATION...Welsh



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.