NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260804_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 08/04 18Z 2.41 2805  77   2  13 0.00
Tue 08/04 19Z 2.17 2706  79   2  14 0.00
Tue 08/04 20Z 1.13 2606  79   2  14 0.00
Tue 08/04 21Z 0.51 2506  78   2  14 0.00
Tue 08/04 22Z 0.32 2405  78   3  15 0.00
Tue 08/04 23Z 0.27 2306  78   6  15 0.00
Wed 08/05 00Z 0.29 2307  77  11  15 0.00
Wed 08/05 01Z 0.31 2308  75  16  15 0.00
Wed 08/05 02Z 0.29 2308  70  22  15 0.00
Wed 08/05 03Z 0.26 2309  65  25  16 0.00
Wed 08/05 04Z 0.26 2309  61  26  17 0.00
Wed 08/05 05Z 0.29 2510  63  27  16 0.00
Wed 08/05 06Z 0.29 2510  65  27  16 0.00
Wed 08/05 07Z 0.27 2609  62  25  16 0.00
Wed 08/05 08Z 0.24 2608  61  22  16 0.00
Wed 08/05 09Z 0.20 2607  57  16  16 0.00
Wed 08/05 10Z 0.18 2606  56  11  16 0.00
Wed 08/05 11Z 0.19 2606  60   7  15 0.00
Wed 08/05 12Z 0.19 2606  63   6  15 0.00
Wed 08/05 13Z 0.17 2505  63   8  15 0.00
Wed 08/05 14Z 0.21 2406  68  10  15 0.00
Wed 08/05 15Z 0.31 2407  72   8  14 0.00
Wed 08/05 16Z 0.37 2407  73   6  14 0.00
Wed 08/05 17Z 0.50 2307  68   4  14 0.00
Wed 08/05 18Z 0.40 2307  61   1  15 0.00
Wed 08/05 19Z 0.56 2307  59   1  16 0.00
Wed 08/05 20Z 0.48 2208  59   1  16 0.00
Wed 08/05 21Z 0.37 2308  61   3  16 0.00
Wed 08/05 22Z 0.37 2310  63  10  16 0.00
Wed 08/05 23Z 0.37 2311  62  22  16 0.00
Thu 08/06 00Z 0.38 2311  64  31  17 0.00
Thu 08/06 01Z 0.36 2411  66  36  17 0.00
Thu 08/06 02Z 0.36 2312  67  41  17 0.00
Thu 08/06 03Z 0.33 2312  64  48  17 0.00
Thu 08/06 04Z 0.34 2412  63  53  17 0.00
Thu 08/06 05Z 0.33 2412  62  57  17 0.00
Thu 08/06 06Z 0.32 2312  62  65  17 0.00
Thu 08/06 07Z 0.37 2314  66  77  17 0.00
Thu 08/06 08Z 0.37 2314  72  86  17 0.00
Thu 08/06 09Z 0.38 2313  78  91  16 0.00
Thu 08/06 10Z 0.35 2312  85  90  16 0.00
Thu 08/06 11Z 0.32 2211  88  91  16 0.00
Thu 08/06 12Z 0.23 2209  89  88  16 0.00
Thu 08/06 13Z 0.20 2108  90  84  16 0.00
Thu 08/06 14Z 0.16 2106  92  77  16 0.00
Thu 08/06 15Z 0.17 2106  94  78  16 0.00
Thu 08/06 16Z 0.16 2106  95  56  16 0.00
Thu 08/06 17Z 0.17 2106  94  41  17 0.00
Thu 08/06 18Z 0.22 2107  92  58  17 0.00
Thu 08/06 19Z 0.30 2109  91  68  17 0.00
Thu 08/06 20Z 0.36 2308  89  63  17 0.00
Thu 08/06 21Z 0.40 2309  84  60  18 0.00
Thu 08/06 22Z 0.40 2310  86  65  18 0.00
Thu 08/06 23Z 0.40 2410  92  57  18 0.00
Fri 08/07 00Z 0.44 2412  92  50  18 0.00
Fri 08/07 01Z 0.54 2415  91  54  18 0.00
Fri 08/07 02Z 0.55 2516  86  52  18 0.01
Fri 08/07 03Z 0.54 2517  88  54  18 0.02
Fri 08/07 04Z 0.45 2715  83  43  18 0.02
Fri 08/07 05Z 0.37 2713  85  39  17 0.01

Run total areal avg QPF for the Central_Greens is: 0.06 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1