Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260210_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)
=== ===== === ==== ==== === === === ====
Tue 02/10 06Z 0.06 3314  55  78  -7 0.00
Tue 02/10 07Z 0.07 3314  58  78  -7 0.00
Tue 02/10 08Z 0.10 3213  61  90  -7 0.00
Tue 02/10 09Z 0.13 3112  75  89  -7 0.00
Tue 02/10 10Z 0.13 3110  84  90  -7 0.00
Tue 02/10 11Z 0.12 3008  83  91  -6 0.00
Tue 02/10 12Z 0.15 2808  77  89  -6 0.00
Tue 02/10 13Z 0.17 2708  71  83  -6 0.00
Tue 02/10 14Z 0.18 2608  63  73  -6 0.00
Tue 02/10 15Z 0.22 2510  51  68  -6 0.00
Tue 02/10 16Z 0.24 2410  41  63  -6 0.00
Tue 02/10 17Z 0.20 2309  39  48  -6 0.00
Tue 02/10 18Z 0.20 2209  40  53  -5 0.00
Tue 02/10 19Z 0.16 2011  43  85  -4 0.00
Tue 02/10 20Z 0.22 2014  49  94  -6 0.00
Tue 02/10 21Z 0.10 1815  91  94  -4 0.00
Tue 02/10 22Z 0.08 1818  95  95  -3 0.05
Tue 02/10 23Z 0.13 1822  96  98  -3 0.06
Wed 02/11 00Z 0.22 1924  96  97  -3 0.07
Wed 02/11 01Z 0.33 2025  96  95  -4 0.06
Wed 02/11 02Z 0.41 2125  98  89  -4 0.05
Wed 02/11 03Z 0.42 2223  98  96  -4 0.04
Wed 02/11 04Z 0.48 2323  97  76  -4 0.05
Wed 02/11 05Z 0.54 2423  97  46  -5 0.03
Wed 02/11 06Z 0.58 2522  97  27  -6 0.02
Wed 02/11 07Z 0.59 2620  97  17  -6 0.02
Wed 02/11 08Z 0.58 2720  97  22  -7 0.01
Wed 02/11 09Z 0.60 2720  97  26  -7 0.01
Wed 02/11 10Z 0.58 2820  97  34  -8 0.01
Wed 02/11 11Z 0.57 2821  96  50  -8 0.01
Wed 02/11 12Z 0.54 2921  95  52  -9 0.01
Wed 02/11 13Z 0.58 2921  96  54  -9 0.00
Wed 02/11 14Z 0.63 2819  96  66 -10 0.01
Wed 02/11 15Z 0.81 2819  96  76 -10 0.01
Wed 02/11 16Z 1.08 2919  95  81 -10 0.01
Wed 02/11 17Z 2.17 2918  95  82 -10 0.01
Wed 02/11 18Z 2.08 2817  96  83 -10 0.01
Wed 02/11 19Z 1.79 2919  96  85 -10 0.02
Wed 02/11 20Z 1.66 2920  95  86 -10 0.02
Wed 02/11 21Z 1.16 3020  95  86 -11 0.02
Wed 02/11 22Z 0.81 3122  96  85 -11 0.02
Wed 02/11 23Z 0.70 3223  95  82 -12 0.01
Thu 02/12 00Z 0.53 3224  95  82 -12 0.01
Thu 02/12 01Z 0.45 3225  95  83 -12 0.01
Thu 02/12 02Z 0.40 3226  96  83 -12 0.01
Thu 02/12 03Z 0.35 3225  96  83 -12 0.01
Thu 02/12 04Z 0.26 3324  96  83 -12 0.01
Thu 02/12 05Z 0.20 3324  95  81 -12 0.01
Thu 02/12 06Z 0.16 3324  94  79 -12 0.00
Thu 02/12 07Z 0.14 3325  93  78 -12 0.00
Thu 02/12 08Z 0.14 3325  93  79 -12 0.00
Thu 02/12 09Z 0.12 3326  93  78 -12 0.00
Thu 02/12 10Z 0.13 3326  93  76 -12 0.00
Thu 02/12 11Z 0.14 3327  93  74 -13 0.00
Thu 02/12 12Z 0.17 3328  93  72 -13 0.00
Thu 02/12 13Z 0.15 3329  93  64 -13 0.00
Thu 02/12 14Z 0.14 3327  92  50 -13 0.00
Thu 02/12 15Z 0.12 3326  92  28 -13 0.00
Thu 02/12 16Z 0.13 3326  90  12 -13 0.00
Thu 02/12 17Z 0.15 3326  86   7 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.70 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