NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260527_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)
=== ===== === ==== ==== === === === ====
Wed 05/27 12Z 0.51 2918  74  42  12 0.00
Wed 05/27 13Z 0.51 2916  78  40  11 0.00
Wed 05/27 14Z 0.53 2814  79  39  11 0.00
Wed 05/27 15Z 0.56 2911  79  34  11 0.00
Wed 05/27 16Z 1.32 2911  80  28  11 0.00
Wed 05/27 17Z 3.46 3010  82  25  10 0.00
Wed 05/27 18Z 2.16 3010  85  28  11 0.00
Wed 05/27 19Z 1.20 3112  84  30  11 0.01
Wed 05/27 20Z 1.27 3114  81  28  10 0.01
Wed 05/27 21Z 1.23 3215  78  20  10 0.00
Wed 05/27 22Z 0.96 3315  74  19  10 0.00
Wed 05/27 23Z 0.47 3316  77  17   9 0.00
Thu 05/28 00Z 0.30 3318  82  19   8 0.00
Thu 05/28 01Z 0.19 3319  88  25   7 0.00
Thu 05/28 02Z 0.15 3419  90  33   7 0.01
Thu 05/28 03Z 0.12 3418  92  41   6 0.01
Thu 05/28 04Z 0.17 3518  93  47   6 0.00
Thu 05/28 05Z 0.17 0018  94  59   6 0.00
Thu 05/28 06Z 0.10 3517  92  68   5 0.00
Thu 05/28 07Z 0.03 3517  90  65   5 0.00
Thu 05/28 08Z 0.04 3418  91  64   5 0.00
Thu 05/28 09Z 0.05 3419  91  58   4 0.00
Thu 05/28 10Z 0.11 3421  88  60   4 0.00
Thu 05/28 11Z 0.12 3422  85  66   4 0.00
Thu 05/28 12Z 0.10 3422  87  71   4 0.00
Thu 05/28 13Z 0.09 3420  91  70   3 0.00
Thu 05/28 14Z 0.14 3419  94  69   3 0.00
Thu 05/28 15Z 0.21 3419  95  68   3 0.00
Thu 05/28 16Z 0.28 3419  95  67   3 0.00
Thu 05/28 17Z 0.36 3420  93  66   3 0.00
Thu 05/28 18Z 0.46 3321  90  70   3 0.00
Thu 05/28 19Z 0.78 3322  89  66   3 0.00
Thu 05/28 20Z 1.18 3321  90  65   3 0.00
Thu 05/28 21Z 0.94 3320  91  72   3 0.01
Thu 05/28 22Z 0.42 3323  93  70   3 0.03
Thu 05/28 23Z 0.27 3326  93  56   3 0.02
Fri 05/29 00Z 0.24 3328  92  44   3 0.01
Fri 05/29 01Z 0.14 3426  94  30   3 0.01
Fri 05/29 02Z 0.18 3426  94  27   3 0.01
Fri 05/29 03Z 0.22 3325  95  28   2 0.01
Fri 05/29 04Z 0.19 3324  97  31   2 0.01
Fri 05/29 05Z 0.14 3422  97  30   2 0.01
Fri 05/29 06Z 0.11 3420  99  36   2 0.01
Fri 05/29 07Z 0.16 3320  98  51   2 0.01
Fri 05/29 08Z 0.25 3320  97  74   2 0.01
Fri 05/29 09Z 0.26 3220  94  72   2 0.00
Fri 05/29 10Z 0.26 3221  89  74   2 0.00
Fri 05/29 11Z 0.24 3222  86  76   3 0.00
Fri 05/29 12Z 0.22 3323  82  79   3 0.00
Fri 05/29 13Z 0.26 3220  79  79   3 0.00
Fri 05/29 14Z 0.42 3118  77  76   2 0.00
Fri 05/29 15Z 1.54 3116  73  75   3 0.00
Fri 05/29 16Z 5.07 3014  74  72   3 0.00
Fri 05/29 17Z 5.63 2911  73  76   4 0.00
Fri 05/29 18Z 6.61 2610  70  85   5 0.00
Fri 05/29 19Z 8.10 2614  68  97   5 0.00
Fri 05/29 20Z 5.62 2714  68  78   5 0.00
Fri 05/29 21Z 6.48 2513  65  87   5 0.00
Fri 05/29 22Z 2.55 2416  71  79   5 0.00
Fri 05/29 23Z 1.21 2421  77  83   5 0.01

Run total areal avg QPF for the Central_Greens is: 0.20 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