NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20250205_0600
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)
=== ===== === ==== ==== === === === ====
Wed 02/05 06Z 0.43 3124  83  10 -17 0.00
Wed 02/05 07Z 0.41 3127  82   6 -17 0.00
Wed 02/05 08Z 0.38 3126  83   6 -17 0.00
Wed 02/05 09Z 0.39 3026  80   8 -17 0.00
Wed 02/05 10Z 0.40 3028  77  10 -17 0.00
Wed 02/05 11Z 0.38 3028  77  12 -16 0.00
Wed 02/05 12Z 0.34 3026  75  13 -16 0.00
Wed 02/05 13Z 0.32 3025  73  16 -16 0.00
Wed 02/05 14Z 0.31 3024  72  18 -17 0.00
Wed 02/05 15Z 0.30 3022  70  20 -16 0.00
Wed 02/05 16Z 0.30 3021  68  20 -16 0.00
Wed 02/05 17Z 0.29 3020  66  14 -16 0.00
Wed 02/05 18Z 0.28 3019  64  10 -15 0.00
Wed 02/05 19Z 0.28 3018  61   8 -15 0.00
Wed 02/05 20Z 0.31 3018  57   8 -14 0.00
Wed 02/05 21Z 0.33 2917  54   7 -14 0.00
Wed 02/05 22Z 0.32 2918  48   7 -13 0.00
Wed 02/05 23Z 0.32 2917  44   9 -12 0.00
Thu 02/06 00Z 0.32 2917  44  10 -12 0.00
Thu 02/06 01Z 0.29 2815  44  12 -12 0.00
Thu 02/06 02Z 0.26 2813  42  14 -11 0.00
Thu 02/06 03Z 0.25 2713  37  16 -10 0.00
Thu 02/06 04Z 0.23 2612  30  16 -10 0.00
Thu 02/06 05Z 0.23 2511  23  16  -9 0.00
Thu 02/06 06Z 0.23 2412  19  15  -9 0.00
Thu 02/06 07Z 0.19 2310  15  14  -8 0.00
Thu 02/06 08Z 0.18 2211  15  13  -8 0.00
Thu 02/06 09Z 0.16 2013  14  14  -8 0.00
Thu 02/06 10Z 0.10 1815  14  21  -7 0.00
Thu 02/06 11Z 0.15 1919  21  35  -8 0.00
Thu 02/06 12Z 0.16 1922  32  58  -8 0.00
Thu 02/06 13Z 0.18 1925  43  87  -7 0.00
Thu 02/06 14Z 0.23 1929  62  96  -8 0.00
Thu 02/06 15Z 0.19 1830  74  91  -8 0.00
Thu 02/06 16Z 0.15 1831  92  94  -6 0.04
Thu 02/06 17Z 0.19 1835  94  96  -5 0.07
Thu 02/06 18Z 0.22 1836  96  97  -5 0.05
Thu 02/06 19Z 0.24 1836  97  97  -5 0.07
Thu 02/06 20Z 0.22 1834  97  83  -4 0.05
Thu 02/06 21Z 0.25 1932  97  61  -3 0.03
Thu 02/06 22Z 0.31 1929  98  52  -3 0.03
Thu 02/06 23Z 0.34 2026  98  23  -2 0.02
Fri 02/07 00Z 0.45 2126  98  13  -3 0.02
Fri 02/07 01Z 0.62 2327  98  13  -3 0.02
Fri 02/07 02Z 0.93 2329  98   1  -4 0.02
Fri 02/07 03Z 1.30 2433  97   2  -5 0.02
Fri 02/07 04Z 1.40 2535  95   3  -6 0.02
Fri 02/07 05Z 1.61 2536  93   4  -7 0.02
Fri 02/07 06Z 1.58 2535  91   6  -7 0.02
Fri 02/07 07Z 1.67 2534  92  13  -8 0.01
Fri 02/07 08Z 1.87 2533  95  17  -9 0.01
Fri 02/07 09Z 1.95 2535  96  31 -10 0.01
Fri 02/07 10Z 2.03 2537  95  36 -11 0.01
Fri 02/07 11Z 1.91 2638  93  56 -11 0.01
Fri 02/07 12Z 2.11 2738  90  43 -12 0.01
Fri 02/07 13Z 7.21 2834  84  38 -13 0.00
Fri 02/07 14Z 14.00 2831  77  35 -14 0.00
Fri 02/07 15Z 17.49 2829  74  34 -15 0.00
Fri 02/07 16Z 19.77 2830  74  39 -15 0.00
Fri 02/07 17Z 19.93 2831  76  48 -15 0.00

Run total areal avg QPF for the Central_Greens is: 0.56 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