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fxus64 ktsa 200138 

Area forecast discussion
National Weather Service Tulsa OK
838 PM CDT Sat Oct 19 2019


The main challenge in the short term will be fog potential and low

Low VFR cigs developed this afternoon over far eastern OK and
western Arkansas and have been slow to erode this evening. If these
clouds hold on, fog potential would be greatly reduced. The hrrr
has trended less aggressive with the fog thru the evening,
especially over northwest AR, which has ME suspicious. Feel more
confident we will have fog development west of the clouds across
portions of NE OK, and the hrrr still suggests some fog here. One
would think that west of the cloud deck there will be favorable
radiational cooling conditions. This, combined with the fact that
dry air advection from the west has stopped, leads ME to believe
there will be fog. I will leave the going fog forecast intact,
showing some Faith that the hrrr will be right with the eventual
erosion of the cloud deck over western Arkansas. Confidence isn't high
enough to issue any headlines attm however. I also made some
tweaks to overnight lows but no major changes.



Previous discussion... /issued 642 PM CDT Sat Oct 19 2019/

concerning taf sites ktul/krvs/kbvo/kmlc/kxna/kfyv/kfsm/krog.
Mostly clear to a few low end VFR conditions should continue into
the overnight hours across much of eastern Oklahoma....while
broken/overcast low end VFR holds over northwest Arkansas through
the evening. Overnight tonight...ceilings are forecast to lower
across northwest Arkansas...with widespread LIFR/IFR ceilings and
visibilities possible late tonight into Sunday morning. Some of
these conditions looks to reach eastern Oklahoma taf sites and
will continue tempo groups for timing. During the day Sunday...the
fog/low stratus clouds should lift and dissipate by late
morning/early afternoon with southerly winds and few/scattered
high clouds for the afternoon hours.

Previous discussion... /issued 343 PM CDT Sat Oct 19 2019/


The main forecast concerns will be fog potential tonight, followed
by severe weather potential with a strong upper storm system and
cold front Sunday night into early Monday. Rain/storm chances with
another storm system and front for the latter half of next week is
also Worth mentioning.

An impulse which brought the showers and a few storms last night
into this morning has lifted off to the northeast. At the surface,
a weak cool front is sliding east across the region in the wake of
the upper disturbance. Moisture is increasing across the region,
especially down over the arklatex. While some drier air is trying
to advect in from the west, models suggest this will stop after
sunset as winds go light beneath the surface ridge. Clearing
skies, light winds and the higher dewpoints all say radiational
fog potential tonight. The NAM and hrrr guidance break out
widespread dense fog across SW MO, southeast Kansas and down into northwest Arkansas and
NE OK after midnight tonight. The NAM would suggest that some fog
potential will extend south of there as well, into southeast OK and west
central Arkansas. Inserted areas of dense fog, with patchy fog mention
in the south where there is more uncertainty.

Now to the meat of this forecast. A strong pv Max currently over
the Pacific northwest, on the nose of a potent cross-Pacific jet,
will dive southeast and then east across the northern and Central
Plains Sunday night. At the surface, a cold front will advance
east/southeast across the region. There are some hints in the data
of a frontal low developing on the front near the nose of the mid
level jet streak in the base of the parent upper low/trough across
south central OK then tracking across southeast OK. Moisture
recovery ahead of the front remains a big question, as most data,
including the GFS and href, suggests that the true warm sector
will not extend much farther north than the Red River. The NAM is
by far the most aggressive with northward advancement of warm
sector, and is an outlier at this point. As such, the magnitude
of this severe event remains in doubt. Showers and storms will
likely begin initiating near the frontal low/triple point with
coverage gradually expanding along the front with time. Kinematic
fields will be easily sufficient to support rotating/organized
storms. The initial development could become supercellular, though
increasingly elevated the farther north you go, with a large hail
and possibly a wind threat. Storms down near the Red River, ie.
Pushmataha and Choctaw counties, will have the best chance of
being near surface-based and would be capable of producing large
hail, damaging winds and a tornado or two. The convective Mode
should trend toward linear with time along the advancing front. The
front should clear the region between 4 and 7 am, ending the
severe weather threat.

Another storm system and front will affect the region beginning
Wednesday night and continuing potentially into Friday. The European model (ecmwf)
has gone back and forth regarding closed low development within
the diving pv Max/shortwave trough during this time frame. The GFS
remains progressive and has been more consistent. What is of
greatest confidence is rain potential with moisture returning and
interacting with the front ahead of the approaching system
Thursday. Raised pops above blended guidance as a result, mainly
Wednesday night and Thursday. Instability will be limited and
confined mainly to the south for this event as it looks now. Rain
chances will taper off by the weekend, though how quickly this
occurs is still a bit uncertain.



Preliminary point temps/pops...
tul 48 78 50 68 / 0 0 80 0
fsm 53 81 55 70 / 0 0 90 10
mlc 49 80 53 69 / 0 0 90 0
bvo 42 77 46 67 / 0 0 90 0
fyv 48 75 51 63 / 10 0 90 10
byv 50 76 53 64 / 20 0 90 10
mko 48 78 50 67 / 0 0 80 0
Mio 46 75 48 64 / 0 0 80 0
f10 48 80 51 68 / 0 0 90 0
hhw 53 81 56 70 / 0 0 90 10


Tsa watches/warnings/advisories...

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