NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260914_0000
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)
=== ===== === ==== ==== === === === ====
Mon 09/14 00Z 0.41 2512  96  51  14 0.00
Mon 09/14 01Z 0.61 2517  95  59  14 0.00
Mon 09/14 02Z 0.75 2622  94  62  14 0.01
Mon 09/14 03Z 0.75 2624  87  65  15 0.01
Mon 09/14 04Z 0.84 2726  94  75  13 0.02
Mon 09/14 05Z 0.95 2826  95  85  12 0.04
Mon 09/14 06Z 1.01 2928  93  84  10 0.03
Mon 09/14 07Z 0.83 2926  84  84  10 0.01
Mon 09/14 08Z 0.96 2926  77  81   8 0.01
Mon 09/14 09Z 0.79 3027  84  49   8 0.00
Mon 09/14 10Z 0.74 3029  90  20   6 0.00
Mon 09/14 11Z 0.58 3130  93   9   6 0.01
Mon 09/14 12Z 0.40 3230  91  12   5 0.01
Mon 09/14 13Z 0.34 3227  89  11   5 0.01
Mon 09/14 14Z 0.34 3225  90   9   5 0.01
Mon 09/14 15Z 0.35 3223  88   7   5 0.00
Mon 09/14 16Z 0.42 3222  87   7   4 0.00
Mon 09/14 17Z 0.50 3221  82   6   4 0.00
Mon 09/14 18Z 1.90 3219  80   7   4 0.00
Mon 09/14 19Z 2.70 3218  77  12   4 0.00
Mon 09/14 20Z 2.41 3218  79  16   4 0.00
Mon 09/14 21Z 1.14 3218  79  18   4 0.00
Mon 09/14 22Z 0.52 3221  78  18   4 0.00
Mon 09/14 23Z 0.39 3222  76  20   4 0.00
Tue 09/15 00Z 0.26 3322  73  21   4 0.00
Tue 09/15 01Z 0.19 3322  72  21   5 0.00
Tue 09/15 02Z 0.14 3322  70  20   6 0.00
Tue 09/15 03Z 0.08 3420  66  16   6 0.00
Tue 09/15 04Z 0.02 3417  62  13   7 0.00
Tue 09/15 05Z 0.02 3415  60  11   7 0.00
Tue 09/15 06Z 0.02 3513  57   9   7 0.00
Tue 09/15 07Z 0.06 0010  50   7   8 0.00
Tue 09/15 08Z 0.05 0008  48   6   8 0.00
Tue 09/15 09Z 0.04 0104  43   6   8 0.00
Tue 09/15 10Z 0.02 0102  40   7   9 0.00
Tue 09/15 11Z 0.03 0901  42   8   8 0.00
Tue 09/15 12Z 0.02 1803  43   9   8 0.00
Tue 09/15 13Z 0.07 2004  44  10   7 0.00
Tue 09/15 14Z 0.10 2106  44  11   7 0.00
Tue 09/15 15Z 0.08 2005  45  12   8 0.00
Tue 09/15 16Z 0.08 2006  47  13   9 0.00
Tue 09/15 17Z 0.13 2008  50  14   9 0.00
Tue 09/15 18Z 0.15 2008  50  14  10 0.00
Tue 09/15 19Z 0.12 1910  47  15  11 0.00
Tue 09/15 20Z 0.21 2012  50  25  11 0.00
Tue 09/15 21Z 0.25 2015  49  16  11 0.00
Tue 09/15 22Z 0.28 2117  43  39  13 0.00
Tue 09/15 23Z 0.28 2118  36  60  14 0.00
Wed 09/16 00Z 0.28 2119  31  89  15 0.00
Wed 09/16 01Z 0.30 2121  27  91  15 0.00
Wed 09/16 02Z 0.34 2123  29  86  15 0.00
Wed 09/16 03Z 0.38 2223  30  86  15 0.00
Wed 09/16 04Z 0.40 2224  31  85  15 0.00
Wed 09/16 05Z 0.47 2325  36  85  14 0.00
Wed 09/16 06Z 0.48 2425  36  87  14 0.00
Wed 09/16 07Z 0.53 2427  43  83  14 0.00
Wed 09/16 08Z 0.56 2428  56  91  13 0.00
Wed 09/16 09Z 0.58 2428  61  89  13 0.01
Wed 09/16 10Z 0.58 2528  75  91  13 0.01
Wed 09/16 11Z 0.57 2528  79  84  13 0.02

Run total areal avg QPF for the Central_Greens is: 0.21 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