Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260210_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 02/10 18Z 0.17 2109  43  70  -5 0.00
Tue 02/10 19Z 0.14 2010  35  90  -4 0.00
Tue 02/10 20Z 0.12 1813  38  98  -5 0.00
Tue 02/10 21Z 0.11 1817  68  95  -6 0.00
Tue 02/10 23Z 0.13 1824  96  98  -3 0.06
Wed 02/11 00Z 0.27 2025  96  98  -4 0.07
Wed 02/11 01Z 0.37 2124  95  98  -5 0.07
Wed 02/11 02Z 0.39 2124  96  95  -4 0.08
Wed 02/11 03Z 0.43 2223  97  94  -4 0.08
Wed 02/11 04Z 0.46 2422  97  93  -4 0.05
Wed 02/11 05Z 0.48 2521  97  57  -5 0.05
Wed 02/11 06Z 0.49 2621  97  16  -5 0.03
Wed 02/11 07Z 0.45 2719  96   3  -5 0.02
Wed 02/11 08Z 0.44 2719  95   3  -6 0.01
Wed 02/11 09Z 0.46 2819  96   5  -6 0.01
Wed 02/11 11Z 0.44 2919  96  39  -7 0.01
Wed 02/11 12Z 0.44 2919  96  50  -7 0.01
Wed 02/11 13Z 0.46 2918  96  63  -8 0.01
Wed 02/11 14Z 0.54 2818  97  75  -8 0.01
Wed 02/11 15Z 0.63 2817  96  82  -9 0.00
Wed 02/11 16Z 0.78 2817  96  85  -9 0.01
Wed 02/11 17Z 1.03 2816  96  85  -9 0.01
Wed 02/11 18Z 1.34 2816  96  85  -9 0.01
Wed 02/11 19Z 1.30 2918  96  86  -9 0.01
Wed 02/11 20Z 1.12 2919  96  86  -9 0.02
Wed 02/11 21Z 0.90 2919  96  83 -10 0.02
Wed 02/11 22Z 0.93 3020  95  82 -10 0.02
Wed 02/11 23Z 0.80 3122  95  81 -11 0.02
Thu 02/12 00Z 0.67 3122  96  81 -12 0.02
Thu 02/12 01Z 0.41 3222  95  83 -12 0.01
Thu 02/12 02Z 0.29 3324  95  83 -12 0.01
Thu 02/12 03Z 0.26 3324  95  84 -12 0.01
Thu 02/12 04Z 0.27 3325  95  83 -12 0.00
Thu 02/12 05Z 0.23 3324  94  82 -11 0.01
Thu 02/12 06Z 0.21 3325  94  79 -11 0.01
Thu 02/12 07Z 0.14 3325  94  76 -11 0.01
Thu 02/12 09Z 0.08 3424  93  78 -11 0.01
Thu 02/12 10Z 0.09 3425  93  77 -11 0.01
Thu 02/12 11Z 0.07 3426  93  75 -11 0.00
Thu 02/12 12Z 0.08 3426  94  74 -12 0.00
Thu 02/12 13Z 0.09 3425  94  69 -12 0.00
Thu 02/12 14Z 0.08 3424  92  67 -12 0.00
Thu 02/12 15Z 0.09 3424  92  68 -12 0.00
Thu 02/12 16Z 0.10 3423  92  68 -11 0.00
Thu 02/12 17Z 0.10 3424  92  64 -11 0.00
Thu 02/12 18Z 0.11 3424  91  62 -11 0.00
Thu 02/12 19Z 0.11 3424  90  58 -11 0.00
Thu 02/12 20Z 0.12 3324  89  48 -11 0.00
Thu 02/12 21Z 0.14 3325  88  31 -11 0.00
Thu 02/12 22Z 0.13 3325  81  16 -11 0.00
Thu 02/12 23Z 0.07 3425  66   8 -10 0.00
Fri 02/13 00Z 0.04 3425  58  11  -9 0.00
Fri 02/13 01Z 0.03 3425  60  13  -9 0.00
Fri 02/13 02Z 0.03 3426  64  14 -10 0.00
Fri 02/13 04Z 0.03 3424  65  14  -9 0.00
Fri 02/13 05Z 0.03 3423  64  14  -9 0.00

Run total areal avg QPF for the Central_Greens is: 0.79 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