NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260221_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 02/21 12Z 0.21 2907  99  83  -7 0.00
Sat 02/21 13Z 0.21 2908  99  82  -7 0.00
Sat 02/21 14Z 0.11 3206  99  74  -7 0.01
Sat 02/21 15Z 0.06 3504  98  74  -8 0.00
Sat 02/21 16Z 0.07 0102  98  75  -8 0.00
Sat 02/21 17Z 0.07 3101  98  80  -8 0.00
Sat 02/21 18Z 0.06 3101  98  82  -8 0.00
Sat 02/21 19Z 0.05 3502  97  80  -8 0.00
Sat 02/21 20Z 0.06 0003  96  75  -8 0.00
Sat 02/21 21Z 0.13 0204  96  70  -8 0.00
Sat 02/21 22Z 0.18 0405  97  66  -8 0.00
Sat 02/21 23Z 0.23 0506  97  66  -8 0.00
Sun 02/22 00Z 0.25 0507  95  62  -8 0.00
Sun 02/22 01Z 0.26 0707  93  59  -8 0.00
Sun 02/22 04Z 0.18 1207  90  55  -8 0.00
Sun 02/22 05Z 0.18 1309  88  53  -8 0.00
Sun 02/22 06Z 0.19 1311  87  51  -8 0.00
Sun 02/22 07Z 0.16 1413  80  58  -8 0.00
Sun 02/22 09Z 0.16 1413  72  65  -8 0.00
Sun 02/22 10Z 0.16 1313  71  71  -7 0.00
Sun 02/22 11Z 0.15 1413  63  78  -7 0.00
Sun 02/22 12Z 0.16 1414  53  84  -8 0.00
Sun 02/22 13Z 0.18 1314  51  89  -8 0.00
Sun 02/22 14Z 0.19 1314  54  92  -8 0.00
Sun 02/22 15Z 0.23 1315  56  91  -8 0.00
Sun 02/22 16Z 0.29 1216  58  87  -8 0.00
Sun 02/22 17Z 0.36 1216  60  89  -8 0.00
Sun 02/22 18Z 0.38 1216  66  92  -8 0.00
Sun 02/22 19Z 0.46 1216  72  92  -8 0.00
Sun 02/22 20Z 0.55 1116  75  91  -8 0.00
Sun 02/22 21Z 0.65 1118  76  91  -8 0.00
Sun 02/22 22Z 0.61 1118  80  88  -9 0.00
Sun 02/22 23Z 0.59 1119  82  86  -8 0.00
Mon 02/23 00Z 0.61 1021  81  81  -8 0.00
Mon 02/23 01Z 0.64 0923  80  74  -8 0.00
Mon 02/23 03Z 0.69 0824  76  49  -8 0.00
Mon 02/23 04Z 0.74 0825  75  48  -9 0.00
Mon 02/23 05Z 0.74 0826  66  66  -8 0.00
Mon 02/23 06Z 0.72 0827  65  70  -8 0.00
Mon 02/23 07Z 0.74 0728  62  67  -8 0.00
Mon 02/23 08Z 0.74 0729  59  70  -8 0.00
Mon 02/23 09Z 0.73 0631  52  75  -8 0.00
Mon 02/23 10Z 0.78 0634  45  80  -8 0.00
Mon 02/23 11Z 0.77 0636  38  82  -7 0.00
Mon 02/23 12Z 0.78 0636  37  84  -7 0.00
Mon 02/23 13Z 0.73 0534  37  83  -8 0.00
Mon 02/23 14Z 0.74 0531  41  86  -9 0.00
Mon 02/23 15Z 0.80 0529  54  86 -10 0.00
Mon 02/23 16Z 0.95 0427  81  87 -12 0.00
Mon 02/23 17Z 0.61 0328  90  86 -12 0.00
Mon 02/23 18Z 0.52 0230  90  86 -11 0.00
Mon 02/23 19Z 0.43 0132  90  86 -10 0.00
Mon 02/23 20Z 0.31 0133  91  86 -10 0.03
Mon 02/23 21Z 0.22 0034  91  87  -9 0.07
Mon 02/23 22Z 0.17 0034  92  87  -9 0.07
Mon 02/23 23Z 0.13 3534  92  87  -9 0.05

Run total areal avg QPF for the Central_Greens is: 0.23 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