NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260512_1200
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 05/12 12Z 0.40 3210  82  46  -3 0.00
Tue 05/12 13Z 1.56 3111  81  37  -3 0.00
Tue 05/12 14Z 3.73 3112  78  34  -3 0.00
Tue 05/12 15Z 5.07 3112  73  35  -3 0.00
Tue 05/12 16Z 5.12 3011  72  38  -2 0.00
Tue 05/12 17Z 5.53 2911  77  37  -2 0.00
Tue 05/12 18Z 5.26 2911  76  34  -1 0.00
Tue 05/12 19Z 5.44 2910  74  31  -1 0.00
Tue 05/12 20Z 4.60 2909  71  29   0 0.00
Tue 05/12 21Z 3.50 3008  69  26   0 0.00
Tue 05/12 22Z 2.40 2907  67  25   0 0.00
Tue 05/12 23Z 0.99 2807  67  25   0 0.00
Wed 05/13 00Z 0.58 2808  67  23   0 0.00
Wed 05/13 01Z 0.52 2707  68  22   0 0.00
Wed 05/13 02Z 0.49 2607  67  18   0 0.00
Wed 05/13 03Z 0.47 2407  67  15   0 0.00
Wed 05/13 04Z 0.50 2308  66  13   0 0.00
Wed 05/13 05Z 0.46 2209  65  12   0 0.00
Wed 05/13 06Z 0.41 2209  61   9   0 0.00
Wed 05/13 07Z 0.50 2212  59  22   1 0.00
Wed 05/13 08Z 0.51 2213  60  55   1 0.00
Wed 05/13 09Z 0.57 2213  67  89   1 0.00
Wed 05/13 10Z 0.37 2013  77  98   1 0.00
Wed 05/13 11Z 0.25 1915  82  99   1 0.00
Wed 05/13 12Z 0.20 1916  87  98   2 0.01
Wed 05/13 13Z 0.20 1919  92  96   3 0.02
Wed 05/13 14Z 0.23 1920  98  95   4 0.05
Wed 05/13 15Z 0.26 1921  94  97   3 0.08
Wed 05/13 16Z 0.18 1826  92  98   5 0.04
Wed 05/13 17Z 0.29 1931  93  97   5 0.02
Wed 05/13 18Z 0.42 2030  95  96   5 0.03
Wed 05/13 19Z 0.43 2027  93  97   5 0.05
Wed 05/13 20Z 0.33 1924  89  90   6 0.01
Wed 05/13 21Z 0.28 1927  91  94   6 0.00
Wed 05/13 22Z 0.31 1929  94  98   6 0.03
Wed 05/13 23Z 0.37 1930  93  94   6 0.03
Thu 05/14 00Z 0.43 1932  90  86   6 0.01
Thu 05/14 01Z 0.50 1933  88  77   6 0.00
Thu 05/14 02Z 0.54 2034  89  84   6 0.00
Thu 05/14 03Z 0.56 2034  88  77   6 0.01
Thu 05/14 04Z 0.54 2033  85  72   6 0.01
Thu 05/14 05Z 0.48 2031  81  77   6 0.00
Thu 05/14 06Z 0.45 2029  75  82   6 0.00
Thu 05/14 07Z 0.37 1927  83  90   5 0.01
Thu 05/14 08Z 0.26 1925  93  94   5 0.01
Thu 05/14 09Z 0.21 1822  95  98   5 0.07
Thu 05/14 10Z 0.15 1822  97  98   5 0.08
Thu 05/14 11Z 0.11 1720  97  92   5 0.04
Thu 05/14 12Z 0.05 1719  98  93   5 0.03
Thu 05/14 13Z 0.07 1618  98  94   5 0.04
Thu 05/14 14Z 0.21 1418  98  97   5 0.03
Thu 05/14 15Z 0.31 1420  98  93   5 0.03
Thu 05/14 16Z 0.31 1418  98  77   5 0.06
Thu 05/14 17Z 0.44 1215  99  69   5 0.04
Thu 05/14 18Z 0.64 1117  99  70   5 0.04
Thu 05/14 19Z 0.76 1018  98  80   5 0.03
Thu 05/14 20Z 0.90 0819  97  89   5 0.02
Thu 05/14 21Z 1.03 0720  94  91   5 0.06
Thu 05/14 22Z 0.89 0722  92  94   5 0.06
Thu 05/14 23Z 0.70 0621  96  94   5 0.06

Run total areal avg QPF for the Central_Greens is: 1.11 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