Request for GEFS v13 to produce freezing spray to help a OPC's milestone

[WenMeng-NOAA]

Logan Dawson from OPC requests freezing spray as GEFS v13 product.

I'll pass along one more update that should be made for the UPP code. From Todd Spindler's interactions with Jim Overland in recent weeks, we found out that some of our codes for the Overland algorithm use an outdated parameter from Jim's original 1986 formulation. In Jim's 1990 paper, Equation 1 defines the PR term as PR = windspeed*(tf - t2m)/(1.+.4*(sst - tf)). It's rather subtle and very easy to miss, but Table 4 in Section 5 of that paper redefines that term as PR = windspeed*(tf - t2m)/(1.+.3*(sst - tf)).

I went through some of our older OPC post-processing code and other references to the algorithm and confirmed the updated 0.3 value is correct. I'm not super well versed in the UPP code, but I think it would only require a one-line change to the CALVESSEL subroutine to correct it there for future GFS, GEFS, etc. implementations. I've already made the change where necessary on OPC's AWIPS system, and in the process, validated that the slight parameter change doesn't completely wreck the calculation or anything of that nature.

[HuiyaChuang-NOAA]

@WenMeng-NOAA I checked the algorithm shown in Logan's email:
l

and believe another fix to UPP may be needed.
PR(i,j)=SPD10(i,j)(-1.7-TSHLTR_C)/(1.+.4(SST_C+1.7))
TSHLTR should be air temperature in the algorithm. However, TSHLTR in UPP is potential temperature
which needs to be converted to temperature prior to computation of PR. If there is a frontal system
moving in, differences could be significant

[WenMeng-NOAA]

@ChristopherHill-NOAA Could you test the changes Huiya commented on? I can provide you the test case for GFS if needed.

[HuiyaChuang-NOAA]

@ChristopherHill-NOAA
To convert 2m potential temperature to 2m temperature, you can reference lines 1606 of SURFCE.f:
https://github.com/NOAA-EMC/UPP/blob/release/gfs_v16/sorc/ncep_post.fd/SURFCE.f#L1606
. My suggestion is to update line 35 of CALVESSEL.f as such:

TSHLTR_C=TSHLTR(I,J)*(PSHLTR(I,J)*1.E-5)**CAPA-C2K

Also, OPC asked to change coefficients. Please see Wen's first comment in this ticket

[ChristopherHill-NOAA]

Following modifications made to CALVESSEL.f by @WenMeng-NOAA in PR #1146, images of ice growth (x 10^5 m/s) were produced from interpolated GFS forecast product (F120) of sample cycle 2020073000 before and after the modification, with another image depicting the significant difference of values resulting from the code modification.

before
after
difference

While GRIB2 documentation simply defines a variable for ice growth (ICEG) over a rate of meters per second, GEMPAK documentation more commonly defines variable IGRO as "rate of ice accretion on vessel in salt water in inches per three hours". To produce the final GEMPAK / AWIPS IGRO product, an additional conversion may be necessary within UPP to conform the product with the expected unit of measure.

[HuiyaChuang-NOAA]

Chris, any chance you can plot the Alaska region? Thank you! Huiya

…

On Tue, Feb 25, 2025 at 5:15 PM Christopher Hill ***@***.***> wrote: Following modifications made to CALVESSEL.f by @WenMeng-NOAA <https://github.com/WenMeng-NOAA> in PR #1146 <#1146>, images of ice growth (x 10^5 m/s) were produced from interpolated GFS forecast product (F120) of sample cycle 2020073000 before and after the modification, with another image depicting the significant difference of values resulting from the code modification. ICEG_2020072700F120_original.gif (view on web) <https://github.com/user-attachments/assets/867a2f0d-0978-46f7-a42b-a49f2b395f00> before ICEG_2020072700F120_modified.gif (view on web) <https://github.com/user-attachments/assets/7653daa6-231e-4da7-9077-76e5b416056e> after ICEG_2020072700F120_difference.gif (view on web) <https://github.com/user-attachments/assets/f843254f-d63e-41c9-9d98-837b98af8fff> difference While GRIB2 documentation <https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table4-2-10-2.shtml> simply defines a variable for ice growth (ICEG) over a rate of meters per second, GEMPAK documentation <https://unidata.github.io/gempak/man/parm/apxA.html> more commonly defines variable IGRO as "rate of ice accretion on vessel in salt water in inches per three hours". To produce the final GEMPAK / AWIPS IGRO product, an additional conversion may be necessary within UPP to conform the product with the expected unit of measure. — Reply to this email directly, view it on GitHub <#1147 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ANQZ2VBTPYQE2JR6HLRJA2L2RTTQ3AVCNFSM6AAAAABXUBXYBSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMOBTGQYTMMZYGY> . You are receiving this because you commented.Message ID: ***@***.***> [image: ChristopherHill-NOAA]*ChristopherHill-NOAA* left a comment (NOAA-EMC/UPP#1147) <#1147 (comment)> Following modifications made to CALVESSEL.f by @WenMeng-NOAA <https://github.com/WenMeng-NOAA> in PR #1146 <#1146>, images of ice growth (x 10^5 m/s) were produced from interpolated GFS forecast product (F120) of sample cycle 2020073000 before and after the modification, with another image depicting the significant difference of values resulting from the code modification. ICEG_2020072700F120_original.gif (view on web) <https://github.com/user-attachments/assets/867a2f0d-0978-46f7-a42b-a49f2b395f00> before ICEG_2020072700F120_modified.gif (view on web) <https://github.com/user-attachments/assets/7653daa6-231e-4da7-9077-76e5b416056e> after ICEG_2020072700F120_difference.gif (view on web) <https://github.com/user-attachments/assets/f843254f-d63e-41c9-9d98-837b98af8fff> difference While GRIB2 documentation <https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table4-2-10-2.shtml> simply defines a variable for ice growth (ICEG) over a rate of meters per second, GEMPAK documentation <https://unidata.github.io/gempak/man/parm/apxA.html> more commonly defines variable IGRO as "rate of ice accretion on vessel in salt water in inches per three hours". To produce the final GEMPAK / AWIPS IGRO product, an additional conversion may be necessary within UPP to conform the product with the expected unit of measure. — Reply to this email directly, view it on GitHub <#1147 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ANQZ2VBTPYQE2JR6HLRJA2L2RTTQ3AVCNFSM6AAAAABXUBXYBSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMOBTGQYTMMZYGY> . You are receiving this because you commented.Message ID: ***@***.***>

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-------------------------------------------------------------- Hui-Ya Chuang Mission Delivery Program Officer Office of Director, National Centers for Environmental Prediction National Weather Service 301-683-3716 Office 4611, 5830 University Research Court College Park. MD 20740