Winter Weather Discussion – 2008-15-2

Valid: 2008-12-15 thru 2008-12-16
Timing: Intermittent

Highlights:

– High to extreme fire danger is possible on Saturday and Sunday for
western Oklahoma. Impacts, will be low as wildfire conditions will be
favorable but limited to western Oklahoma.

– An Arctic cold front will move through the state late Sunday
afternoon and during the overnight hours. Temperatures and wind
chills values will rapidly drop a short time after frontal passage.
Impacts, will be to high-profile vehicles on east/west roads due to
strong northerly winds. Temperatures may remain near or below
freezing for several days.

– Freezing rain/drizzle and sleet are possible Sunday night into
Monday morning across Oklahoma. Northwest Oklahoma stands the best
chance of getting a measureable amount, which appears to be sleet.
Impacts, low overall but roadways will be highly impacted as any ice
accumulations will make driving nearly impossible.

– Snow and sleet are possible on Tuesday across the northern half of
Oklahoma. Additional winter precipitation is possible Wednesday –
Thursday, but forecast confidence remains low.

Discussion:

First off, while a big weather change is on the way and we'll be cold
for several days; I do agree with the NWS that a significant winter
weather event is not on the horizon. However, the forecast for
mid/late next week remains complex.

D2 – Saturday

Strong southerly winds will develop across the state on Saturday as
the western U.S. longwave trof develops. 12z NAM shows temperatures
in the mid 60s in western Oklahoma with dewpoints in the low 30s.
Wildfire conditions will be present, but not particularly extreme at
this point. If a fire weather watch or warning is issued, I'll update
this.

D3 – Sunday

Strong southerly winds will continue on Sunday with additional
warming. However, moisture will be increasing statewide and should
offset some of the wild fire conditions present in western Oklahoma.

Later in the afternoon an Arctic cold front is expected to plunge
across the state into the overnight hours. I'm going with model
average right now which brings the front into NW OK during the
afternoon hours, through OKC early evening and out of the state during
the overnight hours.

D4 – D5 (Monday – Tuesday)

The 12z GFS is a keeper and is close with the 12z ECMWF on mid-level
features. There remains some surface issues but I'm sticking with the
GFS surface pattern, to include the temperature profile. As such, a
prolonged period of cold weather is on-tap for the state as some areas
will spend several days below freezing. Along with this is the
potential for a variety of precipitation types. Starting off on
Monday a weak shortwave trof should result in freezing drizzle and
sleet for parts of the state, mainly the northern half. GFS shows low
QPF in northern sections if at all. But given what happened on
Tuesday, I'm keeping POPs in the forecast for Monday morning.
Precipitation threat should clear by Monday afternoon. 12z NAM has no
QPF at this time period. There is continued lift during the afternoon
but moisture appears to decrease which would seem to limit
precipitation chances.

GFS shows another shortwave trof moving into northwest Oklahoma and
Kansas on Tuesday. Moisture returns at 925mb/850mb and GFS QPF maxes
out across northwest Oklahoma. The 540 line is right on this area and
so guessing snow or sleet will be difficult. I'd certainly think that
sleet potential will extend almost to Oklahoma City at this point.

D6 – D7 (Wednesday – Thursday)

Tuesday's wave moves out of the area during the afternoon hours and
things quiet down for a little bit. Forecast confidence in the D6-D7
range is quite low for a variety of reasons. 1) expected atmospheric
temperature profile as the models want to warm up the surface. The
GFS MOS and model plot data disagree with my bet on the temperature
plot, which shows a high around 28F in OKC due to reinforcing cold air
surge. This would fit the 500mb pattern as a shortwave trof moves
south out of central Canada into North Dakota on Wednesday. With all
the model disagreement, I'm not pinning my forecast on any one
meteorological outcome. However, my current thinking is we'll remain
much colder than MOS indicates and in-line with Norman NWS's forecast
from this morning. 2) The 12z GFS now shears a shortwave trof across
the area on Wednesday and another piece on Thursday, the prior runs
had one system ejecting northeast on Thursday. I'm not sure if this
is a trend or flip-flop, for now will just monitor. There remains
potential for winter precipitation Wednesday – Thursday and this is in
the current Norman/Tulsaa NWS forecast packages (ZFP). Unfortunately
until the cold air is in-place Monday morning and sampled by the upper
air RAOB system, model issues regarding the temperature profile will
continue. This is a major reason why the forecast is so muddy.

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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