Category Archives: Texas

GOES-13 outage, GOES-R IFR products still produced with GOES-15

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GOES-R IFR Probabilities computed with GOES-West during the morning of Sep 24 2012

GOES-13 was placed in standby after experiencing an anomaly on Sunday, so all GOES-R IFR Probabilities are being computed with GOES-West data;  GOES-15 is in FD mode, acquiring a full disk each half hour to provide coverage for CONUS.  GOES-15 data did detect the development of fog/low stratus over southern/coastal Texas and Louisiana overnight under the presence of light winds and high dewpoints.  The regions of highest probabilities correspond well with IFR conditions.  The 1330 UTC image, at the end, shows a noticeable drop in coverage as the daytime predictors replace the nighttime predictors (this includes using the visible imagery as a cloud mask).

Fog over the Texas Panhandle

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GOES-R IFR Probabilities, and Surface Visibility/Ceilings, from 0432 UTC through 1432 UTC on 22 August 2012

GOES-R IFR Probabilities showed good spatial correlation with observed IFR conditions early in the morning on 22 August 2012.  The spatial characteristics of the field suggest that model-only predictions of the presence of fog/low stratus occurred in regions over west Texas that were overlain by higher clouds.  The Traditional brightness temperature difference product at 1101 UTC, for example, below, shows the characteristic signal of high clouds over parts of west Texas.  There is also a significant region of returns over north central OK/south central Kansas that is not associated with IFR conditions.  The GOES-R IFR product in that region correctly shows low probabilities.

Brightness Temperature Difference from GOES (10.7 – 3.9) at 1101 UTC 22 August.

The upper-air sounding from Amarillo from 1200 UTC confirms the presence of saturated conditions only in the boundary layer.

Skew-T/Ln P Thermodynamic diagram frmo 1200 UTC 22 August 2012 at Amarillo TX

Isolated Fog/Low Stratus in Texas

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GOES-R IFR Probabilities computed using MODIS data (upper left), MODIS Brightness Temperature Difference (the ‘traditional’ Fog Product) (upper right), Lowest 1km Relative Humidity from the NAM (lower left), MODIS IR Window Channel (lower right)

The MODIS-based GOES-R IFR probability image, above, showed a region of high probabilities of IFR over Bandera and Real Counties in Texas west of San Antonio.  This signal is driven by the brightness temperature difference (shown, upper right) and the relative humidity in the Rapid Refresh.  The NAM relative humidity is shown in the lower left image, and the signal in the GOES-R IFR field suggests the RAP relative humidity is similar.  Note how the brightness temperature difference signal farther west in the image does not lead to a signal in the IFR Probabilities;  model relative humidities there are lower.

Does the high probability of IFR signal verify?  In other words, when you see an isolated signal like this, how much credence can you give it?  Hondo, TX (HDO), just southeast of the higher IFR probabilities, does not show IFR conditions.  How do things evolve with time?  GOES-based imagery, below, show the expansion of the IFR probabilities from 0800 UTC, the approximate time of the MODIS pass, above, to 1030 UTC.  The expansion is typical of what would occur with radiational fog formation overnight.  By 1100 UTC, ceilings at Hondo (HDO) and Rocksprings (ECU) are near IFR conditions.  It appears that the IFR probability signal is correctly diagnosing the slow development of a  fog/stratus deck.

GOES-R IFR Probabilities (Upper left), Ceilings and Visibility plotted over GOES-R Cloud Thickness (upper right), GOES-East enhanced Window Channel brightness temperature (bottom left), GOES-East Brightness Temperature Difference (bottom right) from 0800 UTC

GOES-R IFR Probabilities (Upper left), Ceilings and Visibility plotted over GOES-R Cloud Thickness (upper right), GOES-East enhanced Window Channel brightness temperature (bottom left), GOES-East Brightness Temperature Difference (bottom right) from 1030-1100 UTC

There was a fortuitous pass of the Suomi/NPP satellite over this region as the fog/low stratus developed.  Does that satellite give any more information about the presence of fog?  The loop below toggles between the GOES-R IFR probability from GOES-East data and the Day/Night Band from VIIRS.  Because the Moon is nearly new, very little moonlight is illuminating the cloud field so it is difficult to determine if fog is actually present at 0832 UTC over the region.  The parts of the counties over which the fog is developing are sparsely populated, so there are no city lights from which to glean information.