GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images (above) revealed unseasonably cold surface infrared brightness temperatures in the -30 to -40ºC range (dark blue to green color enhancement) across much of Montana on the morning of 03 March 2019. Overnight low temperatures at a number of first-order reporting sites were colder than -30ºF (-34ºC) — with the coldest location across the state (and the entire US, including Alaska) dropping to -44ºF (-42ºC). This was only 1ºF warmer than the all-time record low for Montana during the month of March (record low: -45ºF at Glasgow in 1897, and at Fort Logan in 1906). A few daily/monthly cold temperature records were set in the Great Falls and Billings areas.

A sequence of 3 consecutive VIIRS Infrared Window  (11.45 µm) images (from NOAA-20 and Suomi NPP) with a different color enhancement is shown below — the red shades indicate surface infrared brightness temperatures of -40ºC and colder.

===== 04 March Update =====

On the morning of 04 March, GOES-16 “Clean” Infrared Window images (above) showed a more localized pocket of very cold surface infrared brightness temperatures over the southwest part of Montana. The coldest measured surface air temperature was -46°F at Elk Park (at an elevation of 6292 feet) —  which, if certified, will establish a new all-time March low temperature record for the state of Montana.

A sequence of 3 consecutive VIIRS Infrared Window images from NOAA-20 and Suomi NPP (below) revealed surface infrared brightness temperatures as cold as -46ºC or -51ºF within the red-enhanced areas.

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Large bushfires burning in the southern portion of the state of Western Australia produced three pyroCumulonimbus (pyroCb) clouds on 01 March 2019. JMA Himawari-8 “Red” Visible (0.64 µm) images (above) showed that the pyroCb clouds drifted southeastward after formation.

Himawari-8 “Clean” Infrared Window (10.4 µm) images (below) further revealed the 3 distinct pyroCb pulses — 2 originating from the southernmost fire located near 29.5ºS / 124.4ºE, and a smaller one originating from a fire located farther to the northwest. Cloud-top infrared brightness temperatures cooled to the -59 to -63ºC range for the pair of larger pyroCbs (which was close to the tropopause temperature of -64ºC on Perth soundings: plot | data) with temperatures reaching -51ºC with the smaller northernmost pyroCb. Also apparent was a surge of cooler air moving northeastward behind a surface trough, whose arrival appeared to coincide with the pyroCb formation. A time series of surface data from Forrest (YFRT) clearly showed the arrival of the cool, moist air behind the trough.

As shown using RealEarth, an overpass of the Suomi NPP satellite provided a more detailed view of the first (and largest) pyroCb at 0537 UTC (above), with NOAA-20 capturing the second pyroCb cloud about an hour later at 0628 UTC (below). The coldest cloud-top infrared brightness temperature on the 0537 UTC Suomi NPP VIIRS image was -70ºC (darker black enhancement); in addition, there appeared to be an Above-Anvil Cirrus Plume associated with that pyroCb, extending southeastward from a subtle Enhanced-V signature at the upshear (northwestern) edge of the cloud (where the warmest temperature was -48ºC, green enhancement).

On Himawari-8 Shortwave Infrared (3.9 µm) images (below), the pyroCb clouds exhibited a warmer (darker gray) appearance compared to adjacent conventional cumulonimbus clouds — this is due to the fact that ice crystals ejected into the pyroCb anvils are smaller (due to their shorter residence time within the intense updrafts above the fires), and these smaller ice crystals are more effective reflectors of incoming solar radiation. The large flare-up of red-enhanced land during the day is due to highly reflective soils of the Great Victoria Desert that quickly become very hot.

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GOES-17 (GOES-West) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) displayed subtle thermal signatures of some of the highest-elevation western and central portions of the Alaska Range on 28 February 2019.

Plots of GOES-17 Water Vapor weighting functions, calculated using 12 UTC rawinsonde data from Anchorage, are shown below. Even with a very large satellite viewing angle (or zenith angle) of 70.1 degrees — which would tend to shift the Water Vapor weighting functions to higher altitudes —  the presence of dry air within the entire mid-upper troposphere brought the weighting function peaks downward to pressure levels corresponding to those of the higher elevations of the Alaska Range.

The dry air aloft helped to provide a remarkably cloud-free day over much of south-central Alaska, as seen in GOES-17 “Red” Visible (0.64 µm) images (below). In addition, an example of the transient spikes in daytime solar reflectance seen during this time of year was evident in the Visible imagery — note the brief brightening of a few of the images centered at 2115 UTC. Additional details about this effect are available here.

Just for fun, a closer look at the GOES-17 Visible imagery (below) revealed the tidal ebb and flow of drift ice within Cook Inlet and Turnagain Arm in the Anchorage area — and a similar diurnal flow of ice was also seen on the following day (animated GIF | MP4).

===== 01 March Update =====

With a similar scenario to the previous day (but farther to the east), dry air aloft allowed thermal signatures of the highest summits of the eastern Alaska Range and the Wrangell Mountains to be apparent in GOES-17 Water Vapor imagery — even the Upper-level 6.2 µm band (above).

However, in this case the Water Vapor weighting functions derived using rawinsonde data from nearby Anchorage were not representative of the pocket of dry air farther east over the mountains. An increase in the moisture profile — especially within the mid/upper troposphere — shifted the weighting functions to higher altitudes, due absorption and re-emission by that higher-altitude (and colder) moisture. Note how the weighting function contributions centered around the 300 hPa pressure level increased during the 24 hours from 12 UTC on 28 February to 12 UTC on 01 March, while the relative contributions decreased within the 500-700 layer (below).

An overpass of the Suomi NPP satellite provided a number of NUCAPS sounding profiles across this region (below).

A comparison of a dry NUCAPS sounding over the mountains (Point D) with a moist sounding near Anchorage (Point M) is shown below. As shown here, the moisture profile of the NUCAPS Point M sounding was similar to that of the 12 UTC Anchorage sounding.

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The National Weather Service (NWS) and NESDIS are implementing a change to the default Mesoscale Domain Sector (MDS) locations for GOES-17. On March 5, at 1500 UTC, MDS #2 will have its default location changed to Alaska, to better serve the Alaska region of the National Weather Service. The image above shows the approximate location of the new default, centered at 56º N, 150º W (versus 35.5º N, 101.5º W). (Link). 

The default location before the switch for MDS #2 is shown in this image from AWIPS.  The toggle below, using SIFT, shows the approximate locations of current and future  default MDS #2.

Mesoscale sectors now and in the near future can be viewed at this site.

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