NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260830_1800
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)
=== ===== === ==== ==== === === === ====
Sun 08/30 18Z 0.88 2716  85  76  11 0.00
Sun 08/30 19Z 1.17 2713  84  85  12 0.00
Sun 08/30 20Z 0.83 2511  86  89  12 0.00
Sun 08/30 21Z 0.61 2413  84  86  12 0.08
Sun 08/30 22Z 0.62 2715  84  67  12 0.10
Sun 08/30 23Z 0.83 2820  87  75  11 0.05
Mon 08/31 00Z 0.86 2822  83  65  11 0.00
Mon 08/31 01Z 0.85 2924  81  39  11 0.00
Mon 08/31 02Z 0.74 3023  88  36  10 0.00
Mon 08/31 03Z 0.56 3123  92  35  10 0.01
Mon 08/31 04Z 0.30 3220  93  48  10 0.03
Mon 08/31 05Z 0.16 3416  85  27  10 0.01
Mon 08/31 06Z 0.09 3514  75   8  10 0.00
Mon 08/31 07Z 0.05 3512  65   4  10 0.00
Mon 08/31 08Z 0.02 3510  57   2  10 0.00
Mon 08/31 09Z 0.02 3410  52   3  11 0.00
Mon 08/31 10Z 0.06 3310  48   2  11 0.00
Mon 08/31 11Z 0.08 3310  45   1  11 0.00
Mon 08/31 12Z 0.09 3210  42   2  11 0.00
Mon 08/31 13Z 0.10 3209  40   1  11 0.00
Mon 08/31 14Z 0.09 3207  43   2  11 0.00
Mon 08/31 15Z 0.08 3105  48   2  11 0.00
Mon 08/31 16Z 0.11 3003  55   4  11 0.00
Mon 08/31 17Z 0.20 2804  60   9  11 0.00
Mon 08/31 18Z 0.29 2604  59  15  11 0.00
Mon 08/31 19Z 0.30 2704  57  24  11 0.00
Mon 08/31 20Z 0.25 2403  58  29  11 0.00
Mon 08/31 21Z 0.34 2604  59  35  11 0.00
Mon 08/31 22Z 0.19 2404  59  36  12 0.00
Mon 08/31 23Z 0.17 2304  62  38  12 0.00
Tue 09/01 00Z 0.21 2305  65  43  11 0.00
Tue 09/01 01Z 0.20 2305  67  49  11 0.00
Tue 09/01 02Z 0.20 2405  67  50  12 0.00
Tue 09/01 03Z 0.17 2404  71  50  12 0.00
Tue 09/01 04Z 0.12 2204  74  46  12 0.00
Tue 09/01 05Z 0.12 2204  78  50  12 0.00
Tue 09/01 06Z 0.10 2104  79  57  12 0.00
Tue 09/01 07Z 0.06 1904  80  65  12 0.00
Tue 09/01 08Z 0.02 1604  80  79  12 0.00
Tue 09/01 09Z 0.06 1505  83  84  12 0.00
Tue 09/01 10Z 0.12 1306  89  91  12 0.04
Tue 09/01 11Z 0.13 1308  92  94  11 0.12
Tue 09/01 12Z 0.24 1211  93  97  11 0.07
Tue 09/01 13Z 0.30 1214  95  93  11 0.16
Tue 09/01 14Z 0.28 1316  94  92  12 0.21
Tue 09/01 15Z 0.29 1321  93  94  12 0.10
Tue 09/01 16Z 0.32 1322  94  95  12 0.02
Tue 09/01 17Z 0.28 1421  95  92  12 0.01
Tue 09/01 18Z 0.22 1420  96  86  12 0.01
Tue 09/01 19Z 0.21 1419  97  84  12 0.02
Tue 09/01 20Z 0.23 1419  98  84  12 0.02
Tue 09/01 21Z 0.24 1421  97  82  12 0.02
Tue 09/01 22Z 0.20 1422  96  75  12 0.02
Tue 09/01 23Z 0.23 1425  95  64  12 0.01
Wed 09/02 00Z 0.22 1425  95  71  12 0.01
Wed 09/02 01Z 0.20 1525  96  84  11 0.01
Wed 09/02 02Z 0.22 1426  95  89  12 0.01
Wed 09/02 03Z 0.22 1424  95  87  12 0.01
Wed 09/02 04Z 0.19 1423  95  85  12 0.02
Wed 09/02 05Z 0.18 1423  94  87  12 0.04

Run total areal avg QPF for the Central_Greens is: 1.21 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