Interesting features along the west coast on 15 August 2017

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

The following loop is the GOES-16 visible (0.64 micron) band centered along the California / Oregon border on the morning of 15 August 2017:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/15aug17/ncal&loop_speed_ms=60

Low clouds exist along the coastline.  Offshore, vortex generation is occuring as the vortices move southward.  Inland, point sources of smoke with plumes drifting west are observed.  Mount Shasta can be seen in the southeast corner of the image with snow at higher elevations.  The shadow associated with the rising sun is readily seen on the western slope of the mountain.

Further south along the coast:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/15aug17/scal&loop_speed_ms=60

We observe a general decrease in the coverage of low clouds as the sun is rising.  Numerous vortices are observed associated with island effects.  The relative motion of low clouds can provide information on regions that experience gap flow.  Identify regions over the land where gap flow appears to exist.  Consider how useful this imagery could be towards visibility and ceiling monitoring and short-term forecasting.

Posted in Aviation Weather, Ceilings, Fog, Island Effects, Orographic Effects, Visibility | Comments Off on Interesting features along the west coast on 15 August 2017

Fires in Pacific Northwest

The Pacific Northwest (PNW), that is, the states of Washington, Oregon, Idaho and Western Montana are experiencing a significant heat wave right now. Air temperatures are scorching hot, with temperatures in the high 90’s and low 100’s. An amplified upper-level ridge has been quite persistent over the PNW, bringing the high temperatures and dry air to the area.

Due to the abnormally dry conditions, fires have been initiated and are scattered within the PNW. Fires can be seen below via two polar products: the Day/Night Band (DNB, 0.7um) and the Imagery Band 4 (I-4, 3.74um). The two products work in complement with one another. The DNB assists in utilizing a sun/moon reflectance model that illuminates atmospheric features, senses emitted lights, and assists with cloud monitoring during the nighttime, while the I-4 band senses the ‘fire hotspots’, areas that exude high brightness temperatures in comparison to the nearby environment. The I-4 band also assists the DNB in differentiating between what emitted lights are city lights, and what lights are the emitted lights from the fires.

It is important to note that the DNB and I-4 band are at two different spatial resolutions; DNB at 750 meters an the I-4 band at 375 meters. The static images can be seen below at 0924Z (0224 local time), 3 August 2017.

DNB

DNB_modified

I-4 Band

I4_modified

Posted in Miscellaneous | Comments Off on Fires in Pacific Northwest

Quasi-Null case for lots of TPW over eastern Colorado on 29 July 2017

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

We’ve shown blog entries that highlight the value of the CIRA advected layer precipitable water (ALPW) product for heavy rain cases.  Here we show a case of very high LPW during the monsoon circulation over western North America that affected eastern Colorado but this time failed to produce excessive rain.

The 1200 UTC Denver sounding on 29 July 2017 was extremely moist:

DNR_12z

This was a near record TPW value for this day of 1.21″ as depicted on sounding climatology for Denver available from SPC:

pw_climo

The ALPW loop covering from near 00 UTC 28 July through 1800 UTC 30 July shows the peak of the monsoon surge of moisture over northeastern Colorado is on 29 July:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/29jul17/lpw&loop_speed_ms=600

While the lower levels are too low for the elevated terrain of most of Colorado, the upper two layers show that the moisture was very deep.  All of this pointed to a threat for potential flash flooding or at least heavy rain for the lower elevations of northeast Colorado on 29 July.

So what actually happened?

Here is a radar loop that spans the mid-day through evening hours:

myanimation

Substantial rain did occur over portions of the mountains west of the Urban Corridor of northeastern Colorado, but these moved very slowly and only light showers managed to move eastward on to the lower elevations.  We can see that heavier showers did develop farther to the east but most of the populated areas along the Urban Corridor failed to receive much rain at all as seen in the CoCoRaHS rainfall reports:

cocorahs

Why didn’t these areas receive heavier rainfall in this abundantly moist atmosphere?  One major factor is that there was so much moisture that the day began under considerable cloud cover.  As the GOES-16 visible (0.64 micron) loop shows, the clouds never cleared over a large portion of northeastern Colorado:

 http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/29jul17/vis&loop_speed_ms=60

Notice that where there was more sunshine further east and south, convection did develop with some flooding issues.  Also, the convection in southeast Wyoming and far northeast Colorado produced what appear to be gravity waves on top of the lower-level cloud cover.

Sometimes, we can still get heavy rain along the Urban Corridor despite cloud cover if upslope is strong and deep, and/or there is a upper level shortwave.  In the absence of these 2 possibilities, another scenario would be storms developing in the adjacent foothills moving eastward, but in this case it appears that the steering flow is very weak.  Looking at the 00Z Denver sounding from 30 July:

DNR_00z

There was drying in the lower levels, and we see there is one westerly wind barb.  It’s possible that the weakening mountain storms sent a weak but fairly large scale outflow (perhaps just above the surface) onto the adjacent plains actually drying the lower levels, since this would be downslope flow.  This stabilization along with the cool temperatures from the persistent cloud cover may have combined to prevent any heavy rains across the Urban Corridor on what appeared to be a day with high heavy rain potential.

Posted in GOES R, Heavy Rain and Flooding Issues, Hydrology | Comments Off on Quasi-Null case for lots of TPW over eastern Colorado on 29 July 2017

Layer PW product for flooding on 27 July 2017

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

During the overnight hours of 26-27 July 2017, a large area in the vicinity of Kansas City received greater than 5″ of rainfall, with maximum amounts around 8.5″ which led to flooding:

precip

GOES-16 10.35 micron imagery during the overnight hours showed a series of convective clusters moving over the same region (northeast Kansas into west-central Missouri):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/27jul17/B13&loop_speed_ms=60

The CIRA layer precipitable water (LPW) product depicted the moisture plumes at different levels that contributed to this flash flood event:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/27jul17/lpw&loop_speed_ms=600

Upper left panel Sfc – 850 mb LPW

Upper right panel 850 – 700 mb LPW

Lower left panel 700 – 500 mb LPW

Lower right panel 500 – 300 mb LPW

At the lowest level (sfc – 850 mb), we observe abundant moisture with origins from the Gulf of Mexico advecting in from the south, along with enhanced moisture convergence along a frontal boundary.

At mid to upper levels, we observe abundant moisture with origins from the tropical eastern Pacific resulting from the North American monsoon circulation.

Abundant moisture throughout a deep layer in the vertical is one of the key ingredients for excessive rainfall that can lead to flooding.  The LPW product provides context for the origins of moisture plumes and allows one to see them “coming together” from an observational perspective.

Posted in GOES R, Heavy Rain and Flooding Issues, Hydrology, POES | Comments Off on Layer PW product for flooding on 27 July 2017