Area Forecast Discussion
Issued by NWS Tulsa, OK

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FXUS64 KTSA 271134

Area Forecast Discussion
National Weather Service Tulsa OK
634 AM CDT Sat May 27 2017

Low clouds currently near a Okemah, Jay line with some patchy fog
developing north of cloud deck. Low clouds will continue to spread
north today with ceiling heights slowly increasing. Strong to severe
thunderstorms will develop over portions of eastern Oklahoma late
this afternoon and spread east during the evening hours. LIFR
conditions will be likely in the stronger cells which was handled
with TEMPO groups.


.PREV DISCUSSION... /Issued 444 AM CDT Sat May 27 2017/

A surface low was positioned over Southeast Colorado...Northeast
New Mexico...and the Oklahoma/Texas Panhandles this morning. From
this low...a frontal boundary extended northeast through the
Plains connecting to a closed low over Central Canada. A second
frontal boundary extended eastward through far Northwest Oklahoma
into far Northeast Oklahoma/far Southeast Kansas through Central
Missouri. Finally...a third boundary...the associated dryline
extended southward from the surface low through Western Texas.
These boundaries will be the main focus for setting up a very
unstable atmosphere with increasing severe potentials late this
afternoon into tonight across Eastern Oklahoma and Northwest

Through this afternoon...the CWA will remain south of the frontal
boundaries to the north and east of the dryline expecting to setup
between I-35 and highway 75 in Central Oklahoma. In response...breezy
southerly winds will continue to transport ample amounts of
moisture into the region with low/mid 70 degree dewpoints likely
across much of the CWA. At the same time...temperatures will
again climb into mid 80s to low 90s for the CWA which will create
heat index values around 100 degrees for parts of Eastern
Oklahoma. These conditions will aid in a very unstable atmosphere
this afternoon...however a strong cap in place should hinder
thunderstorm develop through much of the afternoon hours.

Late this afternoon into this evening...latest model solutions
continue to indicate a weakening of the cap which would allow for
thunderstorm initiation to quickly develop along 1.) the frontal
boundaries becoming one cold front pushing southeastward and/or
2.) the dryline just west of the CWA. At this time...early on
thunderstorm development looks to be more discrete
cells...especially for any development along the dryline as shear
vectors are expected to be perpendicular to the dryline. The more
discrete cells will likely become severe as storms tap into steep
mid level lapse rates...40-60kt deep shear vectors and excessive
amounts of CAPE. Thus...the potential for very large
hail...damaging winds as well as a tornado potential will be
possible. The greater tornado potential looks to be more based on
intersecting boundaries and or strengthening storms creating their
own near storm environment. Through the early evening
hours...locations for the greater storm development potential
looks to be across Northeast Oklahoma close to the triple point
into Southeast Oklahoma near the dryline.

Overnight tonight...thunderstorm development is progged to spread
across the CWA as the cold front enters into the region and
overtakes the dryline late tonight. The front looks to be
near/just south of the I-44 corridor after midnight and moving
into far Southeast Oklahoma and across Western Arkansas early
Sunday morning. Storm mode during the night looks to become more
linear to a possible MCS diving southeast along and ahead of the
cold front as shear vectors become more parallel to the boundary.
In response...this should allow for severe potential to transition
to a damaging wind threat with also a continued large hail
potential across Southeast Oklahoma and Western Arkansas.
Also...with the ample moisture over the region...heavy rainfall
will be possible with amounts in the 1 to 2 inch range for some
locations. By late tonight...behind the cold front...precip
chances should taper off from northwest to southeast with breezy
northwesterly winds common.

During the day Sunday...the cold front is forecast to exit the
region with the remaining thunderstorm activity shifting east of
the CWA by Sunday afternoon. An upper level trof axis associated
with the closed low over South Central Canada looks to move
through the region Sunday afternoon and evening which should begin
to clear skies from west to east over the CWA. Cooler and more
comfortable conditions are forecast behind the front with
temperatures more closer to the seasonal average.

Memorial Day through next week...sunny conditions and near
seasonal average temperatures look possible into the first part
of the week. By mid week and into the later part of the
week...model solutions begin to diverge on details of a series of
shortwaves that look to move into the Plains. Thus...will continue
with previous forecast and keep small chances for thunderstorms
each day Wednesday through Friday.




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