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Area Forecast Discussion (AFD)

Issued by Denver/Boulder, CO (BOU)

                            
000
FXUS65 KBOU 251010
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
410 AM MDT Tue Jun 25 2019

.SHORT TERM...(Today and tonight)
Issued at 410 AM MDT Tue Jun 25 2019

Colorado will be under a moderate westerly flow aloft today 
with continued warming temperatures. Water vapor imagery showing 
some cloudiness across much of the Great Basin with an 
approaching wave coming out of California. This subtle feature 
will be moving across Colorado this afternoon and evening and help
to aid in thunderstorm development today. Lower levels of the 
airmass are still rather dry as forecast soundings showing mainly
inverted-v type soundings. This environment will result in mainly
strong and gusty winds but not a lot of rain with the showers.

Temperatures will warm another 3 to 5 degrees as 700mb 
temperatures climb to around +13c this afternoon. Main change was 
to add at least isolated pops for all of northern Colorado as high
resolution models and simulated satellite imagery showing a fair 
amount of weak convection traversing all of the plains through 
this evening. Main focus still looks to be over the Palmer Divide 
through this evening. Again, main impacts with the storms today 
will be strong and gusty winds up to 50 mph. 

.LONG TERM...(Wednesday through Monday)
Issued at 410 AM MDT Tue Jun 25 2019

Whatever showers were generated Tuesday evening should be long 
gone by 12Z Wednesday morning as weak flow aloft becomes more 
southwest and dries out. A slow moving trough off the Northwest 
U.S. coast will continue to influence our weather the rest of this
week. Initially the trajectories at 500 mb originate over the 
Pacific and desert southwest, resulting in meager moisture 
advection in the mid and upper levels. PW values bottom out on 
Thursday around 0.25-0.35" across the plains. Low level moisture 
is also lacking Wed-Friday as persistent high pressure across the 
west slope will force a surface pressure gradient that favors 
westerly downslope east of the Continental Divide. Thus, 
precipitation chances outside of the high country Wed-Fri will be
low and temperatures will be seasonably hot. 700 mb temps warm to
around +15 degC on Wednesday, and possibly as warm as +17 degC on
Thursday and Friday. With strong mixing temperatures should top 
90 degrees Thursday and Friday, and come close or just touch 90 
degrees on Wednesday. One exception to the the plains remaining
dry could be Wednesday afternoon across the northeast corner. 
Some of the guidance advects low level moisture out of the 
southeast into the far northeast corner, ahead of a dryline. Shear
profiles look weak enough that supercell convection is not 
anticipated, but if 55-60 degF dewpoints make it west into the 
northeast corner, significant instability would exist and pose a 
threat of severe hail Wednesday afternoon. The chances look pretty
low for now, so will just include a slight chance of 
thunderstorms. In the higher terrain, just isolated chances of 
thunderstorms each afternoon, probably generating more gusty winds
that accumulating rainfall. The best chances of measurable rain 
would be south of I-70 in the mountains, Park County, and the 
Palmer Divide, but overall chances are much lower than in the past
weeks.

If you are into free water for your landscaping, this weekend
holds some promise as rain chances will be on the increase. Most 
models bring the Pacific Northwest trough onshore Friday, which 
builds a strong downstream ridge across the middle part of the 
CONUS. On Saturday the Canadian and GFS models both advect mid- 
level moisture from Mexico and New Mexico into colorado. As a 
result, PW values increase into the 0.8-1.0" level across the 
plains. Low-level moisture seems to lag the arrival of the mid- 
level moisture, and as a result the available instability, while 
present, will probably be limited. Wind shear and the mean winds 
aloft are weak with the ridge just downstream, so the main threat 
could be heavy rainfall and gusty winds, though overall coverage 
of the convection may be limited. Saturday and Sunday afternoons 
and evenings look similar in terms of convective chances and 
potential impacts. Storms should fire on the higher terrain and
Palmer Divide and move slowly east with 10-20 kts of southwest 
steering flow. Temperatures should still reach 90 degrees on 
Saturday across the Plains given the late arrival of moisture and
delay in the convective clouds rolling off the mountains. With 
more moisture in place throughout Sunday, feel cloud cover should
be enough to hold highs close to or just under 90 degrees other 
than the northeast corner of the state. The EC is the outlier in 
terms of precipitation chances, essentially keeping the atmosphere
much drier than the other models through Sunday. Uncertainty 
about moisture return this weekend is thus higher than normal and 
PoPs will be kept in check for the time being.

On Monday the models really diverge on moisture content, and 
confidence in a warming vs. cooling trend and precipitation is 
very low. All long range models generate some light precipitation 
across our area in the afternoon, but they also depict a building 
Four Corners ridge of high pressure. While moisture can get 
trapped in the ridge or be advected from the northwest around the
top ridge, it's too far out to determine if either scenario is
possible. Without a clear picture, the blended solution will 
suffice with cooler/wetter weather for Monday. 

Overall, despite the multiple 90+ degree days in the forecast, 
winds should remain light enough to preclude any serious fire wx 
concerns in the extended period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 410 AM MDT Tue Jun 25 2019

Main change to current and next TAF cycle was to add some mention
of thunderstorms (VC/TEMPO) with likely impact of strong and 
gusty winds, especially at APA/DEN. Convection likely to fire over
the Palmer Divide and outflow winds expected to increase from the
south and southeast by late afternoon through early evening.  

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Entrekin
LONG TERM...Schlatter
AVIATION...Entrekin