Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260221_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 02/21 06Z 0.07 1910  96  83  -6 0.00
Sat 02/21 07Z 0.19 2110  97  77  -7 0.00
Sat 02/21 08Z 0.24 2308  98  82  -7 0.01
Sat 02/21 09Z 0.25 2408  98  91  -7 0.01
Sat 02/21 10Z 0.24 2607  98  91  -7 0.02
Sat 02/21 11Z 0.18 2905  98  93  -7 0.02
Sat 02/21 12Z 0.14 3004  98  90  -7 0.01
Sat 02/21 13Z 0.10 3202  98  84  -7 0.01
Sat 02/21 14Z 0.08 0002  98  77  -7 0.01
Sat 02/21 15Z 0.08 0302  98  71  -7 0.00
Sat 02/21 16Z 0.11 0402  98  69  -8 0.00
Sat 02/21 17Z 0.12 0501  96  69  -8 0.00
Sat 02/21 18Z 0.11 0501  93  67  -8 0.01
Sat 02/21 19Z 0.11 0403  89  61  -8 0.00
Sat 02/21 20Z 0.13 0404  86  54  -8 0.00
Sat 02/21 21Z 0.14 0405  83  49  -8 0.00
Sat 02/21 22Z 0.18 0505  80  47  -8 0.00
Sat 02/21 23Z 0.22 0606  78  48  -8 0.00
Sun 02/22 00Z 0.26 0707  76  47  -8 0.00
Sun 02/22 01Z 0.28 0808  77  45  -8 0.00
Sun 02/22 02Z 0.29 0909  75  42  -8 0.00
Sun 02/22 03Z 0.30 1010  65  41  -7 0.00
Sun 02/22 04Z 0.31 1111  51  40  -7 0.00
Sun 02/22 05Z 0.30 1313  47  39  -7 0.00
Sun 02/22 06Z 0.29 1415  46  41  -8 0.00
Sun 02/22 07Z 0.26 1415  49  46  -8 0.00
Sun 02/22 08Z 0.22 1516  52  52  -8 0.00
Sun 02/22 09Z 0.19 1515  55  56  -7 0.00
Sun 02/22 10Z 0.18 1414  55  59  -7 0.00
Sun 02/22 11Z 0.19 1413  52  64  -7 0.00
Sun 02/22 12Z 0.19 1413  51  68  -7 0.00
Sun 02/22 13Z 0.20 1413  52  65  -7 0.00
Sun 02/22 14Z 0.22 1314  53  67  -7 0.00
Sun 02/22 15Z 0.24 1314  57  65  -7 0.00
Sun 02/22 16Z 0.27 1314  60  64  -7 0.00
Sun 02/22 17Z 0.31 1214  64  61  -7 0.00
Sun 02/22 18Z 0.33 1313  69  59  -7 0.00
Sun 02/22 19Z 0.36 1313  72  62  -7 0.00
Sun 02/22 20Z 0.39 1313  75  67  -7 0.00
Sun 02/22 21Z 0.40 1213  76  73  -8 0.00
Sun 02/22 22Z 0.39 1213  77  76  -8 0.00
Sun 02/22 23Z 0.43 1113  79  76  -8 0.00
Mon 02/23 00Z 0.47 1015  80  71  -8 0.00
Mon 02/23 01Z 0.50 0916  80  66  -8 0.00
Mon 02/23 02Z 0.52 0918  78  55  -7 0.00
Mon 02/23 03Z 0.56 0921  78  59  -8 0.00
Mon 02/23 04Z 0.54 0921  72  50  -7 0.00
Mon 02/23 05Z 0.51 0921  62  57  -7 0.00
Mon 02/23 06Z 0.53 0922  55  63  -7 0.00
Mon 02/23 07Z 0.49 0822  52  70  -7 0.00
Mon 02/23 08Z 0.48 0722  48  74  -6 0.00
Mon 02/23 09Z 0.50 0724  44  76  -6 0.00
Mon 02/23 10Z 0.55 0727  38  78  -6 0.00
Mon 02/23 11Z 0.58 0730  34  75  -6 0.00
Mon 02/23 12Z 0.59 0632  34  77  -6 0.00
Mon 02/23 13Z 0.60 0632  34  80  -6 0.00
Mon 02/23 14Z 0.59 0531  34  77  -7 0.00
Mon 02/23 15Z 0.55 0528  38  76  -7 0.00
Mon 02/23 16Z 0.53 0426  42  72  -8 0.00
Mon 02/23 17Z 0.48 0426  50  79  -9 0.00

Run total areal avg QPF for the greens is: 0.10 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