NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260926_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)
=== ===== === ==== ==== === === === ====
Sat 09/26 12Z 0.81 0526  60   5   8 0.00
Sat 09/26 13Z 0.85 0527  62   5   8 0.00
Sat 09/26 14Z 0.83 0527  63   5   8 0.00
Sat 09/26 15Z 0.90 0526  62   8   8 0.00
Sat 09/26 16Z 0.86 0522  59  17   9 0.00
Sat 09/26 17Z 1.09 0519  60  21   9 0.00
Sat 09/26 18Z 3.21 0418  64  25   8 0.00
Sat 09/26 19Z 3.93 0418  64  36   8 0.00
Sat 09/26 20Z 4.26 0419  63  38   8 0.00
Sat 09/26 21Z 2.51 0522  60  51   8 0.00
Sat 09/26 22Z 1.42 0524  60  60   8 0.00
Sat 09/26 23Z 1.14 0526  61  69   8 0.00
Sun 09/27 00Z 1.04 0528  61  83   8 0.00
Sun 09/27 01Z 1.13 0531  61  86   8 0.00
Sun 09/27 02Z 0.97 0531  65  89   8 0.00
Sun 09/27 03Z 0.87 0632  72  94   9 0.00
Sun 09/27 04Z 0.84 0633  80  93   9 0.01
Sun 09/27 05Z 0.84 0634  80  94   8 0.01
Sun 09/27 06Z 0.94 0637  77  93   8 0.01
Sun 09/27 07Z 0.95 0637  71  93   8 0.01
Sun 09/27 08Z 0.95 0637  73  92   8 0.01
Sun 09/27 09Z 0.89 0636  78  86   8 0.01
Sun 09/27 10Z 0.86 0637  85  81   9 0.01
Sun 09/27 11Z 0.80 0638  92  89   9 0.03
Sun 09/27 12Z 0.76 0739  95  90  10 0.05
Sun 09/27 13Z 0.80 0742  97  93  10 0.09
Sun 09/27 14Z 0.82 0743  98  94  10 0.18
Sun 09/27 15Z 0.80 0742  97  82  11 0.16
Sun 09/27 16Z 0.72 0839  96  70  12 0.06
Sun 09/27 17Z 0.67 0835  96  44  12 0.03
Sun 09/27 18Z 0.69 0833  96  38  11 0.02
Sun 09/27 19Z 0.68 0832  96  56  11 0.02
Sun 09/27 20Z 0.68 0832  95  65  11 0.02
Sun 09/27 21Z 0.69 0832  95  59  11 0.02
Sun 09/27 22Z 0.69 0833  95  66  11 0.02
Sun 09/27 23Z 0.65 0833  95  72  11 0.02
Mon 09/28 00Z 0.64 0934  95  72  12 0.02
Mon 09/28 01Z 0.61 0934  94  52  12 0.02
Mon 09/28 02Z 0.60 0934  94  63  12 0.02
Mon 09/28 03Z 0.59 0933  95  60  11 0.02
Mon 09/28 04Z 0.56 0932  93  62  12 0.02
Mon 09/28 05Z 0.53 1031  92  71  12 0.02
Mon 09/28 06Z 0.52 1030  91  69  12 0.01
Mon 09/28 07Z 0.51 1030  92  61  12 0.01
Mon 09/28 08Z 0.50 1029  93  65  12 0.01
Mon 09/28 09Z 0.48 1028  93  68  12 0.01
Mon 09/28 10Z 0.47 0927  93  72  12 0.01
Mon 09/28 11Z 0.46 0926  91  76  12 0.01
Mon 09/28 12Z 0.46 0926  93  78  12 0.01
Mon 09/28 13Z 0.44 0924  92  81  12 0.01
Mon 09/28 14Z 0.40 0922  91  76  12 0.01
Mon 09/28 15Z 0.39 0820  93  78  12 0.00
Mon 09/28 16Z 0.35 0818  94  86  12 0.02
Mon 09/28 17Z 0.31 0715  94  89  11 0.01
Mon 09/28 18Z 0.29 0713  95  91  11 0.01
Mon 09/28 19Z 0.29 0612  97  85  10 0.02
Mon 09/28 20Z 0.28 0612  97  83   9 0.01
Mon 09/28 21Z 0.27 0512  97  82   9 0.02
Mon 09/28 22Z 0.25 0511  97  85   9 0.01
Mon 09/28 23Z 0.23 0610  97  83   9 0.01

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