Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 171011

Area Forecast Discussion
National Weather Service Norman OK
411 AM CST Sat Feb 17 2018

The main focus continues to be periodic rain chances, occasional low-
end fire weather potential, and a challenging temperature
forecast. Only minor changes were made to the previous forecast.

Early this morning, radar mosaic showed a large area of stratiform
light rain oriented west-southwest to east-northeast across the
area. A classic warm advection/isentropic ascent regime atop remnant
cold airmass is the driver for this precipitation event. Increased
moist southerly flow and resultant deep isentropic ascent is in
response to transient shortwave trough emerging from the Rockies. As
this shortwave quickly moves east, our low level flow will veer and
precipitation will shift east. By late morning, precipitation will
likely have exited southeast sections of our area and the rest of
the day will be dry. Despite building mid-level heights/subsidence
and at least partial clearing, some weak low level cold advection
will likely preclude a more substantial warmup. Nevertheless, most
locations will approach or reach 60 degrees for a high temperature
which is around 5 degrees above normal for mid February.

A fairly substantial and quick northward shift of higher low-level
theta-e values will occur Sunday in response to an amplifying upper
flow pattern and strengthening ascent in the northern Plains and
Great Lakes regions. A well-defined warm front will quickly shift
north of the area by late Sunday leaving us in weakly confluent low-
level flow with anomalous moisture. This general pattern suggests
rain showers which could become quite numerous. One limiting factor
to a more widespread rain event is only weak upglide within
strengthening low-level jet since the frontal slope will be well
north of the area and we`ll be in the warm sector. Meager
instability may support some thunder Sunday night, particularly
across the southeast portion of the area. Instability will be
insufficient for severe thunderstorms.

A little more forcing for ascent will overspread the area Monday and
Monday night as amplified mid-upper trough approaches from the west.
We have the highest precipitation probabilities on Tuesday in the
southeast as forcing from upper trough peaks and moisture becomes
highly anomalous for the time of year. We also continued mention of
thunder given weak instability. By Tuesday evening a cold front
should move through and this is where uncertainty grows since
deterministic and ensemble spread in the medium range guidance
grows. Precipitation should have mostly shifted east by then but
there`s some signal for low-level flow to turn easterly and weak
warm/moist advection atop shallow sub-freezing layer that could
support some wintry precipitation in the southeast portion of the
area late Tuesday night into early Wednesday. Confidence is low at
this time.

Regardless of what position, timing, and geometry troughs have by
the end of the week, low-level flow will turn southerly by then and
moisture is likely to substantially increased. We have broad brush
low probabilities of precipitation (slightly above climatological
PoP) for that time period for now and will refine as models
converge onto a similar solution.



Elevated to near critical fire weather conditions are expected
across northwest Oklahoma this afternoon and again Sunday
afternoon. A broader area of western Oklahoma and western north
Texas could see elevated to near critical fire weather conditions
Monday afternoon.

Winds will remain northerly today and could peak at around or just
above 15 mph today with gusts up to 25 during peak heating/mixing
in northwest Oklahoma. Despite the northerly winds, temperatures
should reach the lower 60s. RH values may fall to around 15
percent or slightly lower. 48 hour rainfall total map from the
Oklahoma mesonet shows the northern edge of beneficial overnight
rains to be from roughly Arnett to Woodward to Medford. North of
this line, fuels remain quite supportive of wildfire spread with
ERC-G values near the 90th percentile. Further south, although
fuels remain dormant, up to one half inch of rain will help lessen
fuel dryness in the near term. We`ll issue a Fire Danger
Statement to highlight the elevated to near-critical conditions
expected across far northwest Oklahoma later this afternoon.

Southerly winds should bring an increase in moisture Sunday
afternoon, but with wind speeds up to around 25 mph and warmer
temperatures, elevated to near critical conditions will again be
reached across northwest Oklahoma.

On Monday, a dryline is expected to sharpen across western
Oklahoma. Its exact position will determine the expansiveness of
elevated to near critical fire weather conditions, as deep mixing
leading to dry and breezy conditions to its west can be expected.



Oklahoma City OK  60  37  64  55 /  10   0  10  30
Hobart OK         63  38  71  55 /   0   0  10  10
Wichita Falls TX  65  40  71  59 /  20   0  20  20
Gage OK           62  38  72  52 /   0   0   0  10
Ponca City OK     60  34  62  55 /  10   0  10  40
Durant OK         61  41  59  55 /  90   0  30  60




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