Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260803_0000
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)
=== ===== === ==== ==== === === === ====
Mon 08/03 00Z 0.15 1823  84  52  15 0.00
Mon 08/03 01Z 0.17 1825  82  59  15 0.00
Mon 08/03 02Z 0.16 1828  80  66  15 0.00
Mon 08/03 03Z 0.17 1928  76  75  15 0.00
Mon 08/03 04Z 0.17 1925  75  83  16 0.00
Mon 08/03 05Z 0.15 1925  74  81  16 0.00
Mon 08/03 06Z 0.11 1824  77  87  16 0.01
Mon 08/03 07Z 0.05 1824  88  96  15 0.03
Mon 08/03 08Z 0.10 1726  94  94  15 0.11
Mon 08/03 09Z 0.14 1728  95  92  16 0.18
Mon 08/03 10Z 0.22 1828  97  88  16 0.30
Mon 08/03 11Z 0.18 1927  97  85  16 0.11
Mon 08/03 12Z 0.22 1926  97  83  16 0.04
Mon 08/03 13Z 0.35 2025  97  84  16 0.01
Mon 08/03 14Z 0.40 2024  97  78  16 0.01
Mon 08/03 15Z 0.45 2023  98  80  16 0.01
Mon 08/03 16Z 0.44 2022  96  79  16 0.01
Mon 08/03 17Z 0.46 2022  92  76  16 0.01
Mon 08/03 18Z 0.63 2021  90  79  16 0.00
Mon 08/03 19Z 1.49 2020  92  82  16 0.01
Mon 08/03 20Z 0.59 2219  95  90  16 0.29
Mon 08/03 21Z 0.75 2424  90  56  15 0.38
Mon 08/03 22Z 0.83 2422  95  48  14 0.02
Mon 08/03 23Z 0.87 2524  97  41  13 0.04
Tue 08/04 00Z 0.77 2723  98  49  12 0.06
Tue 08/04 01Z 0.75 2926  98  74  12 0.07
Tue 08/04 02Z 0.69 3129  99  86  11 0.11
Tue 08/04 03Z 0.55 3231  98  91  11 0.10
Tue 08/04 04Z 0.55 3232  92  67  11 0.02
Tue 08/04 05Z 0.67 3232  90  28  10 0.01
Tue 08/04 06Z 0.83 3129  84   8  10 0.00
Tue 08/04 07Z 0.73 3228  79   6  10 0.00
Tue 08/04 08Z 0.57 3224  74   4  11 0.00
Tue 08/04 09Z 0.51 3222  71   4  11 0.00
Tue 08/04 10Z 0.47 3220  70   4  11 0.00
Tue 08/04 11Z 0.46 3119  67   3  11 0.00
Tue 08/04 12Z 0.43 3119  63   2  12 0.00
Tue 08/04 13Z 0.40 3118  60   3  12 0.00
Tue 08/04 14Z 0.37 3117  57   2  12 0.00
Tue 08/04 15Z 0.41 3115  60   2  12 0.00
Tue 08/04 16Z 0.46 3013  61   2  12 0.00
Tue 08/04 17Z 0.59 3011  62   2  12 0.00
Tue 08/04 18Z 0.58 2910  60   1  13 0.00
Tue 08/04 19Z 0.43 2808  56   1  14 0.00
Tue 08/04 20Z 0.29 2807  50   1  15 0.00
Tue 08/04 21Z 0.24 2706  45   2  15 0.00
Tue 08/04 22Z 0.21 2606  41   2  16 0.00
Tue 08/04 23Z 0.19 2506  38   3  16 0.00
Wed 08/05 00Z 0.21 2407  39   3  16 0.00
Wed 08/05 01Z 0.22 2308  39   2  16 0.00
Wed 08/05 02Z 0.24 2308  42   1  16 0.00
Wed 08/05 03Z 0.29 2310  50   1  16 0.00
Wed 08/05 04Z 0.34 2311  55   1  15 0.00
Wed 08/05 05Z 0.32 2410  54   1  15 0.00
Wed 08/05 06Z 0.29 2310  49   1  15 0.00
Wed 08/05 07Z 0.25 2310  49   1  15 0.00
Wed 08/05 08Z 0.27 2310  51   1  15 0.00
Wed 08/05 09Z 0.27 2310  54   1  15 0.00
Wed 08/05 10Z 0.30 2411  57   1  15 0.00
Wed 08/05 11Z 0.31 2410  62   1  14 0.00

Run total areal avg QPF for the greens is: 1.94 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