Area Forecast Discussion
Issued by NWS Goodland, KS

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942
FXUS63 KGLD 281147
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
547 AM MDT Fri Jul 28 2017

.SHORT TERM...(Today through Sunday night)
Issued at 359 AM MDT Fri Jul 28 2017

Main forecast issue will be chance of thunderstorms and possibility
of heavy rainfall. Satellite showing an amplified pattern over most
of the Pacific. The flow from the eastern Pacific through the
country is a little less amplified and more progressive. Currently
stationary front lies just to the west and south of the area with a
very moist air mass aloft.

At mid levels...The Canadian was doing a little better than the
other output Sref looks to be doing the best at the surface. Models
tended to not catch the low level thermal very well with the Gfs
doing a little better than the other output.

Models, even the high resolution/Cams, did/were not catching
overnight thunderstorm activity very well. Which means the output
may not take into account those mesoscale affects. Overall with poor
recent performance of model output in this weak flow/forcing and
high moisture/instability pattern, confidence in the forecast
through the period is below average.

Today/tonight...Initial question will be how much overnight the
convection will affect this periods forecast. At this time it looks
like overnight convection end by 12z. However will keep watching and
will adjust if needed. In regards to the fog, the latest model
output fits the thinking of the evening shift, and made only a minor
adjustment to the fog forecast.

Questions then become where do thunderstorms form and far east do
they move. For later this afternoon into early this evening a weak
right rear quadrant is just north and west of the area. Models at
mid levels show short wave ridging over the area with the main lift
north and west of the area most of the period. Because of the
ridging in the area the steering flow is anemic. As a result of
the models differ mainly on how far east take the thunderstorms.

Based on where the ridging aloft is and the best lift being to the
east of our area, believe the brunt of the rainfall will be along
and west of the Colorado border. Based on how the rainfall went last
night and weak lift persisting into the overnight hours, believe
that some rainfall will make it across most of the area. What
models do agree on is the highest chance of precipitation happens
after midnight and tried to trend the forecast that way.

Precipitable water vales are 1.50 to near 2.00 inches. Considering
the slow storm movement, locally heavy rainfall and flash flooding
will be possible. However it is hard to pinpoint exactly where all
the heavy rainfall be but based on reasoning above and especially
considering the recent poor model performance, our eastern
Colorado counties definitely have the best chance. Will definitely
have this mentioned in the HWO.

Depending on how the clouds work out, my forecast high temperatures
may end up too warm. However even if have a little break,
temperatures should end up being fine.

Saturday/Saturday night...It is possible that convection may be
ongoing at the beginning of the period. Builder gave me chance
pops in the morning and can see it happening. However, am thinking
that pops may be a little high in the morning.

During the night a weak right rear quadrant is near the far northern
portion of our area. Much stronger lift moves across in the
afternoon through the night. The way all the models are producing
convective feedback issues, not sure if the shortwave is
convectively induced, an actual shortwave trough moving into the
area or a combination of both. No matter the source, the high pops,
especially during the night look warranted.

Precipitable water values remain above 1.5 and are still approaching
2.00 especially over the southern half of the area. Again with the
very slow storm movement, an above average threat of locally heavy
rainfall and flash flooding looks to exist.

Models are all over the place with temperatures and are being very
badly affected by convective feedback issues. Right now am siding
toward the cooler but not the coolest guidance.

Sunday/Sunday night...Uncertainty increases. Models keep a mid
level/convectively induced circulation over the area through at
least the evening. Am thinking that the builder is keeping pops
around too long during the night but am willing to let the slight
to low chance pops continue until have more certainty.

All the models are cooler on Sunday, it is just a question of how
cooler. Kept what the builder had for now. If rainfall stops soon
enough in the night and mid/upper level cloud cover decreases fast
enough, should see a lot of fog given the moist low level air
mass and light winds. However it is far enough out, I can wait on
adding that until later forecast.

.LONG TERM...(Monday through Thursday)
Issued at 359 AM MDT Fri Jul 28 2017

Monday-Tuesday: 500mb high height center over Nevada helps to bring
weak NW flow aloft. With abundant low level moisture in place and
shortwaves traversing the area, CWA will see a chance for showers
and thunderstorms through the period. Best chance for precip will be
along and west of the CO/KS border. Temps will be below normal, with
highs on Monday struggling to get above 80.

Wednesday-Thursday: Upper level ridge over the Rockies amplifies
into Canada bringing a more northerly upper level flow to the
region. As drier air filters into the region, will only see slight
chance of PoPs on Wednesday and essentially none on Thursday. Temps
will remain at or just below normal for the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 536 AM MDT Fri Jul 28 2017

For KGLD...VFR conditions expected through the period. With
daytime heating, expect gusty winds starting at 18Z. Storms
progress east from CO during the late afternoon and evening.
Terminal may see rain or thunderstorm, but had more confidence in
VCTS, especially since timing looks to be outside of the first 12
hours of forecast. Will be closely monitored by next shifts.

For KMCK...VFR conditions and winds less than 12kt expected
through the period. Expect main axis of storms in CO to remain
well off to the west and not impact the terminal through the
period.


&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...BULLER
LONG TERM...SME
AVIATION...SME



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