NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260528_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)
=== ===== === ==== ==== === === === ====
Thu 05/28 12Z 0.05 3514  88  80   5 0.00
Thu 05/28 13Z 0.08 3414  91  77   4 0.00
Thu 05/28 14Z 0.14 3415  92  79   4 0.00
Thu 05/28 15Z 0.16 3416  91  76   4 0.00
Thu 05/28 16Z 0.34 3416  87  72   4 0.00
Thu 05/28 17Z 1.51 3317  82  68   4 0.00
Thu 05/28 18Z 1.78 3319  76  61   4 0.00
Thu 05/28 19Z 1.66 3420  77  59   4 0.00
Thu 05/28 20Z 0.91 3420  83  58   4 0.00
Thu 05/28 21Z 0.72 3319  83  55   4 0.00
Thu 05/28 22Z 0.80 3320  85  58   5 0.00
Thu 05/28 23Z 0.31 3323  91  78   4 0.03
Fri 05/29 00Z 0.07 3427  90  58   4 0.02
Fri 05/29 01Z 0.09 3526  92  47   4 0.00
Fri 05/29 02Z 0.12 3524  93  44   3 0.00
Fri 05/29 03Z 0.03 3524  92  44   3 0.00
Fri 05/29 04Z 0.03 3422  93  35   2 0.00
Fri 05/29 05Z 0.10 3422  94  33   2 0.00
Fri 05/29 06Z 0.13 3421  93  37   2 0.00
Fri 05/29 07Z 0.24 3321  92  45   3 0.00
Fri 05/29 08Z 0.34 3222  90  77   3 0.00
Fri 05/29 09Z 0.37 3223  83  86   3 0.00
Fri 05/29 10Z 0.37 3223  74  78   2 0.00
Fri 05/29 11Z 0.39 3224  72  80   2 0.00
Fri 05/29 12Z 0.36 3222  70  82   2 0.00
Fri 05/29 13Z 0.45 3219  74  81   2 0.00
Fri 05/29 14Z 1.08 3116  75  75   2 0.00
Fri 05/29 15Z 4.50 3014  75  73   3 0.00
Fri 05/29 16Z 5.51 2911  76  78   4 0.00
Fri 05/29 17Z 5.66 2709  76  69   5 0.00
Fri 05/29 18Z 6.02 2511  73  84   5 0.00
Fri 05/29 19Z 6.81 2514  66  96   6 0.00
Fri 05/29 20Z 4.13 2618  66  86   6 0.00
Fri 05/29 21Z 6.55 2616  63  86   6 0.00
Fri 05/29 22Z 0.78 2520  83  70   5 0.03
Fri 05/29 23Z 1.23 2425  86  82   5 0.01
Sat 05/30 00Z 1.26 2425  87  91   5 0.02
Sat 05/30 01Z 0.82 2522  98  94   5 0.09
Sat 05/30 02Z 0.76 2818  98  98   3 0.12
Sat 05/30 03Z 0.55 3119  92  93   1 0.06
Sat 05/30 04Z 0.43 3119  87  75   0 0.02
Sat 05/30 05Z 0.26 3216  93  64   0 0.01
Sat 05/30 06Z 0.14 3315  90  40   0 0.01
Sat 05/30 07Z 0.12 3513  90  31   0 0.00
Sat 05/30 08Z 0.24 0214  95  66   0 0.02
Sat 05/30 09Z 0.56 0522  97  86  -1 0.09
Sat 05/30 10Z 0.95 0729  98  75  -1 0.05
Sat 05/30 11Z 0.89 0730  98  83  -1 0.06
Sat 05/30 12Z 0.69 0526  98  91   0 0.06
Sat 05/30 13Z 0.65 0524  94  93  -1 0.06
Sat 05/30 14Z 0.70 0420  89  92  -1 0.04
Sat 05/30 15Z 2.01 0316  90  78  -1 0.00
Sat 05/30 16Z 2.68 0114  89  63  -1 0.00
Sat 05/30 17Z 2.88 0114  87  49   0 0.00
Sat 05/30 18Z 3.23 0214  86  42   0 0.00
Sat 05/30 19Z 2.36 0215  87  50   0 0.00
Sat 05/30 20Z 2.03 0116  87  67   0 0.00
Sat 05/30 21Z 2.20 0117  84  77   0 0.00
Sat 05/30 22Z 2.07 0117  80  80   0 0.00
Sat 05/30 23Z 0.82 0117  80  79   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.80 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