NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260528_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 05/28 00Z 0.07 3512  74  89  10 0.00
Thu 05/28 01Z 0.05 3514  72  81   9 0.00
Thu 05/28 02Z 0.06 0014  72  86   9 0.00
Thu 05/28 03Z 0.12 0113  75  88   8 0.00
Thu 05/28 04Z 0.10 0112  78  93   8 0.01
Thu 05/28 05Z 0.07 0011  80  89   7 0.00
Thu 05/28 06Z 0.04 3511  84  89   7 0.00
Thu 05/28 07Z 0.07 3511  84  84   6 0.00
Thu 05/28 08Z 0.09 3513  86  82   6 0.00
Thu 05/28 09Z 0.11 3514  88  76   5 0.00
Thu 05/28 10Z 0.09 3516  90  73   5 0.00
Thu 05/28 11Z 0.08 3516  91  70   4 0.01
Thu 05/28 12Z 0.11 3516  93  69   4 0.01
Thu 05/28 13Z 0.16 3416  92  67   3 0.00
Thu 05/28 14Z 0.42 3417  91  65   3 0.00
Thu 05/28 15Z 1.26 3318  89  65   3 0.00
Thu 05/28 16Z 1.98 3320  88  64   3 0.00
Thu 05/28 17Z 2.29 3420  86  63   3 0.00
Thu 05/28 18Z 1.81 3319  88  69   3 0.02
Thu 05/28 19Z 2.14 3320  89  70   4 0.01
Thu 05/28 20Z 1.81 3322  90  66   4 0.02
Thu 05/28 21Z 1.22 3323  90  61   4 0.01
Thu 05/28 22Z 0.68 3325  92  69   4 0.02
Thu 05/28 23Z 0.45 3426  92  62   3 0.02
Fri 05/29 00Z 0.33 3425  92  47   3 0.01
Fri 05/29 01Z 0.28 3424  93  39   3 0.00
Fri 05/29 02Z 0.28 3424  92  35   2 0.00
Fri 05/29 03Z 0.29 3424  91  38   2 0.00
Fri 05/29 04Z 0.26 3424  90  41   2 0.00
Fri 05/29 05Z 0.27 3423  91  43   2 0.00
Fri 05/29 06Z 0.28 3421  91  49   2 0.00
Fri 05/29 07Z 0.32 3320  92  57   2 0.00
Fri 05/29 08Z 0.40 3319  92  68   2 0.00
Fri 05/29 09Z 0.42 3220  94  81   2 0.00
Fri 05/29 10Z 0.46 3219  95  85   2 0.01
Fri 05/29 11Z 0.43 3119  93  76   2 0.00
Fri 05/29 12Z 0.36 3118  87  81   3 0.00
Fri 05/29 13Z 0.28 3217  79  74   3 0.00
Fri 05/29 14Z 0.31 3216  74  67   3 0.00
Fri 05/29 15Z 0.48 3114  72  67   3 0.00
Fri 05/29 16Z 1.88 3011  69  76   4 0.00
Fri 05/29 17Z 4.11 2810  68  83   4 0.00
Fri 05/29 18Z 5.43 2512  70  83   5 0.00
Fri 05/29 19Z 6.19 2415  70  90   5 0.00
Fri 05/29 20Z 8.37 2417  67  90   6 0.00
Fri 05/29 21Z 4.59 2523  73  94   5 0.03
Fri 05/29 22Z 1.43 2424  76  91   4 0.01
Fri 05/29 23Z 1.34 2523  84  94   3 0.02
Sat 05/30 00Z 0.72 2321  91  95   4 0.08
Sat 05/30 01Z 0.66 2321  95  97   4 0.11
Sat 05/30 02Z 0.69 2617  97  93   3 0.13
Sat 05/30 03Z 0.63 3019  95  92   1 0.09
Sat 05/30 04Z 0.53 3119  91  79   0 0.03
Sat 05/30 05Z 0.40 3218  94  59   0 0.02
Sat 05/30 06Z 0.40 3216  95  43  -1 0.01
Sat 05/30 07Z 0.28 3315  97  52  -1 0.02
Sat 05/30 08Z 0.20 3516  97  63  -1 0.03
Sat 05/30 09Z 0.36 0218  97  74  -1 0.04
Sat 05/30 10Z 0.48 0424  98  87  -1 0.05
Sat 05/30 11Z 0.63 0528  97  84  -1 0.05

Run total areal avg QPF for the greens is: 0.87 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